Specifications and +12V Rails
Before diving right in to this review, we think it would be appropriate to present some sort of background information on +12V rails, since that will undoubtedly be the main theme here. If you’ve read our comprehensive explanation of how a power supply works, you probably have a good understanding of what exactly rails are and why the +12V rail is important. If you haven’t, we strongly suggest you do that now, else much of what is about to be relayed might not make sense.



There are several steps electricity has to go through before it is ready to power your computer. Your power supply is responsible for getting it to that point, and those steps can be read about in detail in our previous article. One of the final steps, however, is very much relevant to this discussion. Inside the transformer, the current is tapped at various voltage levels, the very same voltage levels that are needed to run a computer. It is at this point, when the physical current is converted into various constituents, that power supply manufacturers begin to “mickey mouse” around. It’s the ugly side of the hardware world, and we hate to see it happen, but it happens nonetheless. Corners are cut, connections are made second rate, and the overall quality of the product is degraded – at the expense of the consumer. Perhaps the saddest part of it all is that there really isn’t much we can do about it. Aside from opening the power supply and taking a close look at it yourself, a task that most people have been persuaded against doing by shiny labels that warn about the risk of electrical shock, you kind of just have to buy the product and hope that it is what it says it is. Luckily, even if a product has been degraded in this manner, chances are that it is still a fine piece of equipment. In fact, there is nothing really dishonest with this practice at all. Without a definitive organization of power supply manufacturing standards, two companies can produce two power supplies with supposedly identical advertised specs that are, in reality, not so.

You see, there is more than one way to get the numbers that are supposed to represent power supply performance. Manufacturers use different methods to get certain features when those methods may not be the best way. The main feature that power supply manufacturers have differing approaches on is “dual +12V rails”. In the aforementioned article we explained how rails are generated from the transformers in the power supply. We gave a general description of how this is done without getting into the details. Well, without really getting any further into the details, there is no standard way by which rails are to be drawn from the transformer. That is to say that there is no limit on how many rails you can take off of one transformer (physical limitations yes, but none provided by a code of any sort), and there is nothing that dictates which rails you can take off of a transformer. Traditional power supplies, such as pretty much every single PSU produced in the last 5 years minus the last 6 months, draw one or two +12V rails and one +5V rail from the transformer. The +3.3V rail is then derived from the +5V rail in a secondary process to produce the three necessary rails for computer operation. However, the same number of rails can be drawn by using only two leads instead of the three in the above scenario. For instance, there could be 1 +12V tap on the transformer that is then split into two +12V rails, and one +5V tap on the transformer that then generates the +3.3V rail. Furthermore, some power supplies have their own dedicated +3.3V rail that is taken directly off of the transformer. The possible combinations, while not limitless, are certainly huge, and therein lies the problem. Everything we know to be true in the hardware world - everything that tells us that we know what we’re talking about - says that having a two dedicated rails on a power supply is more effective than having two rails that are derived from one. As far as we know there are no tests showing this exactly, but it is more in the principle than the result. If you claim to have dual +12V rails that are really just the same rail split in two, then you don’t really have dual +12V rails do you? Well, you kind of do… but at the core there is only one +12V rail taking the load of two +12V rails, right?

This is the big “dual +12V rails” conundrum we have been alluding to for about the last 4 paragraphs. Why does it exist? Why would a power supply manufacturer knowingly produce units utilizing this inferior design? There are two potential reasons we can think of, but only one that would seem probable. Firstly, perhaps the manufacturers do not know how to do tap two +12V rails. We consider this highly unlikely considering a company whose engineers do not know how to do this have no business producing power supplies. The more likely reason in our minds is that it is easier and more cost-effective to do so. In recent months we have seen the emergence of power supplies with not 2, but 3, 4, and even 5 +12V rails. While the genuineness of these rails are not something we can make judgment on without taking a good look at the power supplies themselves, it is abundantly clear that not all of these rails are “the real thing”.

So then, when Cooler Master sent us this Real Power Pro 850W power supply with 6 +12v rails to test, we had plenty reason to be skeptical. The only thing we could do was open it up and see for ourselves whether or not these rails were the real deal.