The next component in our lineup is the power supply unit, or PSU. The PSU was an often overlooked item in the gaming system build, but no more. In fact, May’s CPU magazine features several articles about power supplies, including two articles on general PSU principles and two sets of reviews (high-end and midrange PSUs). I’ve been getting really lucky lately, finding articles on the components I happen to be looking at that moment — I hope the trend continues.

The last time I built a computer, the case I purchased had a power supply already installed. Good deal, right? Think again! The PSUs that come pre-installed in cases are typically not what a serious enthusiast is looking for (better cases will not come with a power supply). If you’re going to build a mid- or high-end gaming rig, don’t even think about buying a case + PSU combo for $45 to $100. Even if the case suits your needs, the PSU is likely to be under-powered and not of high enough quality for running a high-end CPU and graphics card. For my build, I ended up spending over $350 on my case and PSU ($165 case and $200 PSU), which is more than my CPU is worth retail.

Why spend so much on such a simple component? All a power supply has to do is feed power to the other, more important components, right? Well, yes and no. For one thing, gaming systems draw an enormous amount of power. You have to remember that a quality gaming desktop pushes hardware more than just about any other computing application out there. If you’re running a dual-core CPU, a high-end graphics card, two gigs of RAM, a couple hard drives, an optical drive, and a few case fans, you’re looking at drawing about 350 to 450 watts of power at peak load. One of the articles in CPU notes that if you want to hit the efficiency “sweet spot,” you’ll want your PSU to be capable of supplying twice the power your system will draw, giving it adequate headroom for really intense power spikes. That “free” 325 watt power supply that came with your case isn’t looking so good now, is it?

So, what do we need to look for in a quality PSU? Here’s a quick list that we’ll drill down on:

• basic build quality
• cable design
• rail design
• efficiency rating
• connectors

As with any component, basic build quality is crucial. Fortunately, with PSUs you can use the manufacturer’s reputation as a reliability indicator moreso than you can with other components. There are maybe half a dozen reputable producers of high-end PSUs in the market today, so that reduces the amount of research you need to do. OCZ, Thermaltake, Antec, and Cooler Master are some of the most popular makers of quality PSUs. Some manufacturers of other quality components are also getting into the PSU game, such as Corsair, who are best known for their high-end memory. (Breaking news: OCZ has recently acquired PC Power & Cooling, merging two of the biggest names in power supplies. Let’s hope this marriage brings the best of both companies together.)

You’d think there wouldn’t be much to discuss about power supply design, but as usual, there is more to it than meets the eye, and plenty of areas for heated discussion. Two of the biggest areas of debate in the PSU world have to do with cable and rail design. One of the more recent PSU design updates is to make cables “modular,” meaning that you can plug individual cables into the PSU when you need them and remove the ones you don’t need. This can be important because, as we’ve seen in our discussion of cases, airflow within the case is critical, and the fewer cables you have the less cluttered your case will be. On the downside, modular cables are less efficient at supplying power because of the modular interface. As can be expected, there are proponents on both sides, some saying that the loss of efficiency is negligible, others saying it is significant. I ended up siding with the non-modular, more efficient crowd. PSUs are all about supplying power efficiently, so why degrade that ability? Plus, I’ve got a nice big case with plenty of cable management options, so having extraneous cables won’t be that big an issue for me. Those of you looking to build a SFF box may see things differently.

The other design debate centers around single vs. multiple rails. In a single rail PSU, all the power available to the unit is passed along a single channel or rail, supplying all the cables coming out of the PSU. In a multi-rail design, the total available power is divided between two or more rails, each with its own dedicated maximum power. The issue here, as I understand it, is that single rails can experience something called “crosstalk,” where a power surge to one component can affect other components on the same rail. In theory, this means that if one component fails, it can adversely affect the other components on that rail. Multi-rail design seeks to eliminate crosstalk by isolating components to different rails so that a problem with one component won’t affect other components. Single rail enthusiasts say that this design limits the efficiency of the PSU, since each rail has only a fraction of the total power being supplied by the unit. If all the components on one rail in a multi-rail design are not drawing the max power for that rail, that extra power is lost because it is not available to components on other rails. In a single rail system, this extra power could be used by the other components, making more efficient use of the total power being supplied by the PSU. Again, I came down on the side of efficiency, and opted for a single rail design.

Efficiency rating is another factor to look for in PSUs. When energy is produced by a power supply, some of it is lost in the form of heat. PSUs loose a LOT of energy in the form of heat. In fact, some of the best-rated PSUs sport an efficiency factor of about 80 to 85%, meaning that 15 to 20% of the total power of the PSU is lost to heat. Make sure that your power supply has at least an 80% efficiency rating for maximum performance.

The last thing to check for when shopping power supplies is the type and number of connectors available. Decent PSUs will have more than enough connectors for your needs, including connectors for your motherboard, the CPU, SATA and IDE hard drives, standard molex connectors, and PCIe connectors for your video card(s). If you think you might build an SLI or Crossfire configuration (two video cards), be sure that the PSU supplies enough PCIe connectors. Most high-end video cards require two six pin PCIe connectors, so if you’re going to have two high-end cards, you’re going to need four PCIe connections. The PSU I chose, the PC Power & Cooling Silencer 750, is called a “quad” PSU because it has four PCIe connectors.

Next time: hard drives, easy choices.