CoolerMaster 850W Real Power Pro PSU

Author: J. Micah Grunert
Editor: Howard Ha
Publish Date: Wednesday, December 13th, 2006
Originally Published on Neoseeker (
Article Link:
Copyright Neo Era Media, Inc. - please do not redistribute or use for commercial purposes.

I think we're beginning to see a shift. A shift from those mostly adequate (though increasingly inadequate) power supplies, to sheer over kill. Not over kill in the sense of a power supply so ridiculously powerful that it's almost inconceivable of who would need such electrical requirements. But rather to the delightfully masterfull engineering of a power supply that will survive whatever is thrown at it. The Cooler Master RS-850-EMBA power supply indicates a shift in that direction.

We've all come to expect good things from Cooler Master, and their power supplies are without a doubt, a mainstay in the rigs of gamers and hardware enthusiasts around the world. In the past, we've haven't had much opportunity to review a whole lot in the way of Cooler Master power supplies. The notable exception being our Cooler Master RS-550-ACLY power supply. A foray into the truly silent PSU market for Cooler Master. Though its 550 Watts of power is a little dated to say the least, it was, and still is a decent power supply. On the other hand, we've seen more Cooler Master cases come through our doors than I can easily count.

The Cooler Master I-Tower 930 case was, and still is, one of the sweetest enclosures I've ever seen. Those hot swappable SATA bays were something out of a rack mount server, right in your living room. And the Cooler Master 632 case I had the opportunity to review just happens to be one of my all time personal favourites. Namely for the air filtration system Cooler Master developed for this enclosure.

But we're talking about power supplies today, and we've got 850 Watts of pure Cooler Master power to review. I can fully expect that 850 Watts of raw, untethered power should pass all of our tests with flying colours. But there may be some smaller, less noticeable details that we'll have to inspect further. Never the less, the Cooler Master RS-850-EMBA should be a decent power supply. Perhaps it may even exceed my higher expectations. We'll just have to wait and see.

So we've got a power supply to look at. Should be pretty standard, right? Well, in some case yes, but in others no. The Cooler Master 850W Real Power Pro is probably one of the higher end power supplies available on the market today. Of course, there's plenty of 750 Watt supplies out there, and even more of lesser ratings. But as certain performance demands are made by PC consumers, it is only expected for the power supply market to follow suit. RAID arrays and CrossFire cards, additional cooling and lighting, and overclocking. All these aspects combined demand pure, clean power. Hopefully, our Cooler Master 850W can deliver. Here's a quick list of some of the specifications for our Cooler Master 850W power supply.

Though some of these specifications may not influence your choice is power supply purchase, there are a select few here that should be regarded as important. The ATX Form Factor is standard of course, but the size of the RS-850-EMBA should be taken into consideration. We'll touch on its dimensions in a little bit. The Voltage Auto Ranging is important, especially for such a high capacity supply, though it's not integral to the supply overall. Current Rating isn't particularly important either, as it is a simple indication of the frequency of current the supply may accept. And since all household current cycles at 60Hz (approximately), the range we are given is more than acceptable. Household current can sometimes dip to down to 30-40Hz, but it's extremely rare. As for pushing up over 60Hz, that's a power surge, and something a surge protected power bar will adjust for. On and on to the efficiency rating. An efficiency rating of greater than 85% is good, as it means that less than 15% of the juice you pump into this power supply will lost as heat. It is possible to get higher efficiency ratings, up near the 95% mark or greater, but unless you want to double the cost of your power supply, it isn't really worth it. And finally, the peak output capacity and peak performance capacity. Being able to crank out 850 continuous watts of power is something only a hand full of power supplies can claim. And being able to over draw up to a full kilowatt of juice helps to keep even the most taxed of systems running smoothly. Though seriously, I honestly doubt that many people could draw a full 1000 watts of power, let alone 850W.


AC Input 115V / 230V / 12A /6.3A 60 / 50Hz  
DC Output 3.3V 5V 12V1 12V2 12V3 12V4 12V5 12V6 -12V 5VSB
Peak Current 25A 30A 18A 18A 18A 18A 18A 18A 0.8A 3.5A
Total Output 191W 720W 6W 15W

 Ah, there we go, the meat and bones of power supply performance. As we drift through this chart, we come to see one great defining feature of our Cooler Master 850W supply, that being the 18A supply across the six 12V rails. Normally, most power supplies might deliver 15 Amps across their 12V rail. Having 18 Amps of available current means being able to feeds more devices per rail. If we look at the different devices in a typical PC, you'll get an idea how important these extra amps are. Case in point, a single hard drive might draw up to 2.5 amps at 12 volts while randomly seeking files. Put it to sleep mode, and that consumption drops to around .015 amps on the 12V rail. Now build some fancy 0+1 Raid array and you begin to understand. Maybe we have 8 SATA drives all running on the same 12V rail. That's 20 amps of current draw on a rail that pumps out 18 amps at its peak. A lesser power supply might not cut it. Toss in a high end processor that draws up to 120 watts, and the latest and greatest in graphics cards that'll pull another 120 watts, and you begin to see how important power delivery across the individual rails is .

But that's just the soul of our Cooler Master 850W Real Power PSU. What about the body?

Well, I've done something you shouldn't try at home. Not only will this void your power supply warranty, but it could be potentially painful. Not fatal in any way mind you, but shocking to say the least. I've opened up our RS-850-EMBA and poked around inside. Again, I don't recommend the home user trying this as you could receive quite the shock, even when a supply is unplugged. But I did see a few things inside our Cooler Master that really impressed me. And there were a few things that didn't.

Perhaps the most obvious aspect of the Cooler Master 850W PSU is the size of its box. No, seriously! Power supplies usually come in boxes barely big enough to hold them. Their wires are all bundled and knotted together, a user manual is tossed in there somewhere, and four screws to attach it to your case if your lucky. But the Cooler Master RS-850-EMBA comes in what can only be termed as a very pretty cardboard crate. But enough about the box, let's look at what came with our supply.

Of course, we get the Cooler Master Real Power 850W supply. And we get a detailed user manual written in eight different languages. Cooler Master tossed in four case screws to help attach our supply to a box. That little desiccant pack keeps everything nice and dry. In fact, it might be a good idea to start tossing those inside a computer case. You know, just to help sponge up any unwanted moisture that could threaten expensive parts. And we get a power cord. But this isn't just any power cord.

In talking with Cooler Master, we were told why they chose to use such a beefy cord. They told us it was because of the added power that the RS-850-EMBA draws. Granted, it can only draw a maximum of 15 amps current. It can only do this because of how house hold circuits are commonly limited to 15 amps. Most people don't have much use for anything over 15 amps, unless your like me, with a small shop full of industrial tools that you'll probably won't find at any home improvement store. But back to the cord. Typically, most PSU chords are of a 18 AWG wire. AWG stands for American Wire Gauge, and it's how wire is measured. The higher the number, the finer the conductor within the cable. The lower the number, the thicker the conductor within the cable. Just take a look at the following pictures as an example.


As you can see, our Cooler Master came with a thick 14 AWG cable. This heftier copper core, which costs 3 times as much as 18AWG cable, means it is far easier for electrons to pass through. Had it been anything above say a 20 AWG, then there would be quite a bit of resistance generated and some considerable amount of heat as a by product. That would mean inefficient use of power, some power loss, and a potential fire hazard. I know, its kinda funny how a higher AWG number means a finer wire, it seems back wards. But in this case, driving an 850W power supply with the biggest cord possible is the right thing to do.


Next up is the warning sticker. I found this very bright little tag over top the power receptacle on our Cooler Master supply. And this stickers right, it can be dangerous to run this power supply beneath its rated power demands. If we were to plug the Cooler Master 850W supply into a wall socket that was rated for 115V at 10A, we could see some problems. The voltage requirements won't make much of a difference if they're off by only a few volts here and there. But the required amperage could cause a power supply to over heat. This supply wants 15 Amps in so it can step up that power to those voltage rails. If it's fed far less than 15 Amps, then it will have to work extra hard to step up or step down that current. This extra work can create loads of heat, and extra heat can shorten the life of a power supply, and perhaps even kill it.

And perhaps just as important is not plugging this supply into a power bar. Now I know we're all guilty of this, but with high wattage power supplies, sharing a single circuit with other appliances can spell trouble. Having your high wattage PSU, a big CRT monitor, coffee machine, mini-fridge, printer, desk lamp and speakers all riding on the same circuit is a bad idea. That will place an unnecessary amount of load upon that circuit and cause the circuit breaker to trip. So it's best to have these high wattage PSUs on a circuit of their own, just for efficiencies sake.

On to the supply itself. And my first big question is . . .  Where's my Power Switch? Again, we had to talk with Cooler Master for this one.  According to Cooler Master's product manager, the lack of the switch was a design decision to avoid damage by an "onrush" of power.  The input current of the PSU is a max of 15amps from 90V AC input on a 100% load, and Cooler Master decided to ensure that every time the power is turned on the PC that the PSU will start with a "warm start".

Despite the missing power switch, there is a single dual colour LED on the rear of the PSU. It glows green when active, and glows red when off. Neat, but not nearlly as useful as a power switch may have been.

The one major draw back with this absence of a switch is how to turn the PSU off safely. There have been occasions where I've screwed up Windows so badly (on purpose mind you) that my only salvation is the power switch on the power supply. Now you could yank the power cord from the supply or wall, but that can create other problems. Occasionally, it can cause power spikes or drops that can damage hardware, and can sometimes even corrupt data if the hard drive is still actively spinning. I don't like this missing switch. My solution is a pretty simple one. I would go to the local home improvement store and buy a wall switch rated to carry 15 Amps. They're out there along with number 14 AWG wire, electrical boxes and a few other parts I'll need. I'd hack together some of the 14 AWG wire with that 15 Amp switch and receptacle. An electrical box and plug to finish things off and I've just built a power switch box for the Real Power Pro 850W. Now the parts in these loosely laid plans may seem simple, but playing around with electrical wiring is something only a qualified individual should do. So be fore warned, there is the potential to cause some damage by doing this, so do your homework and before you decide to start playing around with electricity.  

Next on our list is the physical size of the Real Power 850W Pro. As you an see, it's quite a bit bigger than your average ATX supply. Here it is pictured next to one of our recently reviewed ThermalTake 750W Tough Power Cable Management PSU. That was a nice supply with modular cables and standard physical dimensions. The Cooler Master 850W Real Power Pro on the other hand, it's a fair bit longer than its cousins.


Cooler Master Real Power Pro 850W 150(W) x 180(L) x 86(H) (mm)
Thermaltake Tough Power Cable Management 750W 150(W) x 160(L) x 85(H) (mm)

As the figures show, the Cooler Master 850W is 20 millimetres, or about an inch longer than other standard ATX power supplies. And though the mounting points are identical (it is a standard) I might find some difficulty trying to stuff this behemoth into a mid-tower ATX case. Its extra size might complicate cable management and air flow issues.

As we start to look inside the 850W Real Power, there are a number of engineering advancements that I quite like. And perhaps the first one I'll touch on are the two blue thermal probes. These thermal probes are supposed to be held down by some plastic heat shrink tubing, a type of soft plastic tube that you can buy at local electronics stores. It's used to seal connections. If one were to be splicing some wires together, they could use heat shrink rather than plain old electrical tape. In this case, the heat shrink tubing was used to securely adhere these two thermal probes to a couple of fins on the heat sinks. Presumably there is a thermal switch buried somewhere in the inner reaches of this power supply. If the supply should start to overheat due to system load, then the thermal switch would pick up the extra heat in the heat sink fins and turn the fan up to high speed. A great option, considering that there are those moments of surfing the web and typing up documents that draws hardly any current from a PSU. Why have a noisy fan running at full tilt all the time?

What else hides inside? Well, I like the dual transformers. They help to step up and step down the current needed to help power your computer and all of its components. Typically, ATX power supplies will have only one transformer. Well, not completely true. There is the primary transformer and then a smaller secondary transformer. But in the case of the Cooler Master 850W, we have two primary transformers and a single smaller secondary transformer. You can identify them in the following picture as they all ave a yellow banding on top of them. As for whether this extra transformer makes any real difference, yes it does. It makes it easier for the supply to crank the voltages and amperages up and or down. Typically, ATX power supplies use a single primary transformer to change the voltage and amperage, and switch its inputs to get different outputs. It's kinda difficult to explain fully, but having that extra transformer in the Cooler Master 850W is somewhat like having a dual core processor. The work is distributed, and is there for more efficient.

I was quite impressed with the quality of heat sinks that Cooler Master used in this supply. Upon inspection, they appear to be pieces of Aluminium T-channel that has been cut to act as heat sinks for the SCRs (Silicon Control Rectifiers). These SCRs can get quite hot, and will burn out if not sufficiently cooled. Good cooling is a must in any power supply. The large 135mm fan helps too.

One other thing I had noticed inside the Cooler Master 850W was this plastic shield. Though not completely necessary perhaps, it does help to prevent the possibility of any components within the supply from touching the metal casing. It wouldn't take much to short out the components inside a power supply, and this plastic shield helps to prevent any accidental sparks from flying. In fact, I accidentally shorted out an open PSU once. The sparks were pretty, but the dead supply was sad.

Most everything else on the Cooler Master 850W is standard. The power connectors are standard, and everyone uses this type of wire loom to help tame the power cables. Though I will say, the Black Chrome finish on the Cooler Master 850W is exquisite.   

I guess it would be a good idea to make sure that the Cooler Master 850W Real Power Pro lives up to its expectations. And we have a couple of methods for doing so. First, I'll take some sound measurements to see how quiet (or how loud) the unit is. It's a pretty simple task. Just find the quietest atmosphere possible and jumper the power supply to life. Then take a couple readings with our Omega HHSL1 sound meter. As for our quite place, I have a bathroom at home can can get down to 28 dbA ambient in the middle of the night. That's more than quiet enough for some accurate sound measurements.

But there was a problem, a little buzzing problem. When I had plugged in our RS-850-EMBA there was this buzzing sound. So, I unplugged it and the buzzing sound persisted until the residual charge in the capacitors had drained away. Once the supply had been completely discharged, it was silent. This buzzing sound, somewhat akin to a mosquito wisping around a quiet room, could only be one thing. There is something loose inside our Cooler Master 850W supply.

Now when I say loose, I don't mean something I can tighten down with a screwdriver. I mean a component that has a notable manufacturing defect. A potential culprit could be one of the three transformers. If one of the steel plates that comprises its body is loose, it will vibrate back and forth with the frequency of the magnetic field generated. All electrical transformers create magnetic fields. And if this magnetic field is constantly fluctuating at 60hz, or 60 cycles per second (household AC current frequency), then a loose metal plate in a transformer may begin to vibrate like a saxophone reed. There may be the off chance that it could be another component that's creating the buzzing sound, but my money is on a bad transformer.

This doesn't necessarily mean that the Cooler Master 850W will fail prematurely or will have problems delivering the juice it promises. It just means you'll have to live with this little buzzing sound coming from your rig, and honestly it isn't that bad. My sound testing was done with the power supply suspended from a wall hook, just to try an eliminate the possibility or any vibrations from the fan. Here's a quick little chart to show what audible effect that buzzing sound had.


Cooler Master RS-850-EMBA Ambient Sound Testing
Ambient Noise Level 28.8 dBA
10cm Distance with Supply Buzzing but Fan off 29.9 dBA
1m Distance with Supply Buzzing but Fan off 29.3 dBA

No just to confirm. As I had mentioned earlier, the buzzing sound will persist until all of the juice in the capacitors has been drained. My ambient reading of 28.8 dBA was taken at 2:30 in the AM with the supply still in its box. I had also used an LED lamp instead of the compact fluorescent bulbs in my bathroom at home. On of the fluorescent bulbs creates a noticeable buzzing sound itself. It's probably on its last leg and should be replaced. So I had an extremely quiet environment for testing with absolutely no sounds polluting my readings. Then, I plugged in the Cooler Master 850W and quickly unplugged it again. The buzzing sound persisted for maybe 20 seconds afterwards until the capacitors had drained.

Now these aren't the final sound measurements. These are just an indication of what the ambient noise level of this particular supply will be when it's plugged in. It will be totally silent if left unplugged of course, but most of us tend to leave our power supplies plugged in all the time. Again, this sound, though small, is some what irritating. Granted, once you drop this supply into a case and push it under a desk the buzzing sound should be hardly noticeable.

But now we should test the Cooler Master 850W with the fan running. Of course it's going to be louder, and that persistent buzzing sound will add to the overall noise level. But again, all of our sound level testing is done with the supplies outside of the case. It would be a totally different story if we had to take sound measurements with the supply inside a case. And there is also the added difficulty of selecting an enclosure that would approximate the sound dampening properties of every case on the market. Never the less, here's the figure I pulled.

Sound Level Comparison Table
  Cooler Master RS-850-EMBA 850W  ThermalTake Toughpower 750W cable management
Thermaltake Toughpower 750W CoolerMaster RS-550-ACLY OCZ GameXStream 700W PSU AeroCool Zero dba 620W
Ambient(dbA) 28.8 28.2 29.2 30.5 30.5 30.5
1 meter from PSU 31.1 34.0 33.2 41.5 34.3 31.0
10cm from PSU 37.2 42.0 38.5 51.4 38.2 32.6

I was surprised! I thought that buzzing noise would have thrown the Cooler Master RS-850-EMBA sound measurements for a loop. I guess it can be expected that we pulled off some low dbA readings. For one, the big 120mm fan in our Cooler Master 850W looks to be of top quality. That helps to keep the noise level down. Second, high frequency sounds don't travel very far. Their very narrow sign wave breaks down quickly. A simple fact of acoustics and audio engineering is that lower frequencies travel farther. Higher frequencies don't travel very far at all. It's nice to see that the Cooler Master 850W is a quiet supply, despite that little buzzing problem.

Now that we have sound testing out of the way, we move onto the voltage testing. For this we use the one item known to man that will test a power supply like no other. Well, it's actually two things in the form of a pair of CrossFire cards. As legend has it, graphics enthusiasts began seeing problems with their power supplies and CrossFire equipped rigs several months ago. Turns out that CrossFire sucks up an extraordinary amount of juice compared to other graphics cards. If you don't have a CrossFire Certified supply running your CrossFire enabled cards, chances are your system will crash during game play. And worse yet, your power supply may die. So, we'll be using our trusted old video test bench rig to test the Cooler Master RS-850-EMBA. Here's the skinny on what parts we used.

Test Setup

And the CrossFire cards we used

All of the following tests we preformed while running 3DMark 2006 with 2 instances of CPU burn-in running in the background. This should more than sufficiently load up both of the ATI GPUs and both cores of our processor. And one more note with one of the supplies tested. With the ThermalTake Toughpower 750W cable management supply we had also tested the connectors at the bus bar on the side of the power supply. The reason for this being that adding connections to a circuit will create some noticeable measurement of resistance. Granted, these differences we found were so negligible that they won't make any real difference. They're just there because I felt it to be important. All of the other measurements were taken from the first connector on the 24 pin motherboard power connector and the first Molex plug on the power cables. Fortunately, there was no difference between the voltage measurements at the cable ends or the 24 pin connector. The only exception being that of the 3.3V voltage rail which we could only take from the 24 pin mother board connector.

To measure the respective voltage rails we used our Mastercraft 052-0060-2 volt meter. This little tools lets us test for voltage, resistance and amperage. Though we're only interested in the voltage readings in this case.

Voltage testing with 3DMark 2006 & CPU burn-in times 2 (error checking removed)

Cooler Master RS-850-EMBA
850W Power Supply
  3.3 Volt Rail 5 Volt Rail 12 Volt Rail
Idle 3.32 Volts 4.99 Volts 12.10 Volts
Load 3.31 Volts 5.015 Volts 12.105 Volts
Thermaltake Toughpower 750W cable management
voltage taken from molex cables
  3.3 Volt Rail 5 Volt Rail 12 Volt Rail
Idle 3.35 Volts 5.09 Volts 12.18 Volts
Load 3.37 Volts 5.09 Volts 12.22 Volts

voltage taken from bus bar
  3.3 Volt Rail 5 Volt Rail 12 Volt Rail
Idle 3.40 Volts 5.10 Volts 12.19 Volts
Load 3.41 Volts 5.11 Volts 12.23 Volts

Thermaltake Toughpower 750W

  3.3 Volt Rail 5 Volt Rail 12 Volt Rail
Idle 3.29 Volts 5.075 Volts 11.95 Volts
Load 3.29 Volts 5.07 Volts 11.96 Volts

Cooler Master RS-550-ACLY

  3.3V Rail 5V Rail 12V Rail
Idle 3.36V 5.08V 11.99V
Load 3.35V 5.10V 11.87V

OCZ GameXStream 700W PSU

  3.3V Rail 5V Rail 12V Rail
Idle 3.32V 5.01V 12.26V
Load 3.31V 5.04V 12.17V

AeroCool Zerodba

  3.3V Rail 5V Rail 12V Rail
Idle 3.44V 5.11V 12.15V
Load 3.43V 5.14V 12.04V

The figures don't lie! The Cooler Master RS-850-EMBA is incredibly stable. Granted, the other supplies in this round up are quite stable as well. But I would prefer to have a power supply that puts out he juice at the voltage stated, and not too far off from that. As you can see, The Cooler Master 850W is near dead on accurate for the 3.3V and 5.0V rails and kicks up only slightly on the 12.0V rail. A boost of 0.1V on the 12V isn't much to worry about. But if we look at the AeroCool Zerodba and its 3.3V rail, running at 3.44V at idle worries me. This added voltage could put some amount of strain on the motherboards VCM (Voltage Controller Module). It is wholly preferable to have a supply that puts out 3.3V on the nose, or any other voltage for that matter.

But the sweetest thing of all is how little the Cooler Master 850W fluctuated between idle and load. The difference is a nominal .01 volts or less. Other power supplies would kick up or kick down the voltage by .1 volts on a specific rail in some instances. The only supply in this group that really compares is the Thermaltake Toughpower 750W. It hardly fluctuated at all. These tests are hinting toward the increased voltage stability we'll be seeing with higher wattage power supplies.

The important thing about this rock solid stability is the official certified support for NVIDIA G80 based video cards.  With this type of capacity you could run 2 SLI G80's without problems.  I know NVIDIA doesn't require more than a 550W PSU in a G80 SLI setup but I assure you that there will be many users who are more comfortable with a beefy 850W Real Power PRO powering their G8800GTX rigs.  We only had a single 8800GTS available at time of testing so I didn't do any testing (two CrossFire cards would have greater draw than a single 8800 GTS), but the stability of the CrossFire testing lends confidence of the stability of this PSU under any circumstances.

What can I say about the Cooler Master 850W power supply?

For one, I was quite impressed with its stability during CrossFire testing. It isn't often that we see a power supply that has such minor variations between its idle and load phases. That being said, the Cooler Master 850W could defiantly tame even the most demanding of rigs. Whether it be CrossFire or SLI, the Cooler Master RS-850-EMBA screams "Bring it on!"

Now I did take a quick peek at the ATI CrossFire Certified Power Supply listings, but didn't see the RS-850-EMBA anywhere. In fact, I didn't see any Cooler Master power supplies in the list. Perhaps ATI is dragging its heels on certifying PSUs for its CrossFire platform. Regardless of whether or not the Cooler Master 850W is on some list or not, the simple fact remains that it passed our CrossFire testing procedures.  The Real Power Pro IS on the SLI certified list however for the G80 no less.

It's pretty silent, despite that little buzzing sound it was making. Though its larger size probably wouldn't bode too well in a mid-tower case design. I'm not saying it's impossible, just that a power supply this big demands a case to match. Hey, I'm certain that Cooler Master would have a big enclosure to fit this beast.

In the end, the Cooler Master RS-850-EMBA 850W power supply is a must for the true hardware enthusiast. If you're someone who lives for RAID arrays full of drives, dual graphics card configurations and a typhoon full of fans, then 850 watts is where you'll want to start. And if you're an overclocker, then you know how important proper voltages are.

The only consideration that has me thinking twice is the $260 USD price tag. That's the asking price for a really good motherboard, or a graphics card or some mid range processor. But in greater consideration, if one were to be building a rig with $1000 worth of graphics bliss, $500 in processor power, so on and so forth with the expensive parts, then shelling out $260 USD probably isn't too much of a big deal. Considering especially that you'd like all of those high end parts to run at their peak of performance.

For the most loaded of rigs, the Cooler Master Real Power Pro 850W RS-850-EMBA is the way to go.


Copyright Neo Era Media, Inc., 1999-2014.
All Rights Reserved.

Please do not redistribute or use this article in whole, or in part, for commercial purposes.