Power Supply

We're going with a 400w power supply for this single CPU setup. It never hurts to have extra power on tap. The most important thing when shopping for a power supply is not just the reported wattage, but the distribution of this power. Old cpus like the 486 used to run primarily off the +5v rail, in contrast the current generation of cpus use a +12v rail. So you need to make sure that the power supply has a robust +12v rail. Some power supplies even have a dedicated +12v rail for the processor. In fact, the new ATX12V version 1.3 protocol calls for more robust +12v rails as compared to prior standards.

Alan: We made initial plans to go with a Fortron/Sparkle Power power supply, probably the best in the low-cost, high-performance price range. Fortron/SPI power supplies are among the best in the industry and you'll find them rebadged in black with a quiet fan as the Zalman PSU. In this system, we've used a SilenX.com 400W PSU. SilenX is a company in Southern California that has begun developing their own power supplies in-house. Normally, we'd be wary of an unproven design house, however SilenX is building it around the Fortron/SPI platform that we trust, and the manufactured is handled by Fortron - this is the same way PC Power and Cooling also custom designs their PSUs.

Basically, SilenX worked with Fortron and contracted power supplies with better heatsinks, larger capacitors, upgraded MOSFETs, and AC line noise filters. This should improve stability of the power supply and SilenX.com also reports having a more stable 12V rail. After production, SilenX adds their own fan design with silicone dampening mounts to reduce the noise. One thing to consider is that the power supply fan is often not the primary source of your system noise, so unless you pair this Silenx power supply with silent system fans, your total system volume may not be much less.

SilenX.com power supply

I had initially planned to use the 460W or 550W SilenX active PFC power supply. SilenX.com let us know that they're very conservative with their power ratings and so we've gone with their 400W Active PFC model.

Going to an Active PFC with power factor > .99, will improve the efficiency of the unit when compared to a passive PFC (80% true efficiency as opposed to 76%). This means there will be just a little bit of extra power when it's needed. Since power supplies only draw power as needed, the Active PFC models should also reduce the current drawn from the wall. For anyone who leaves their system on 24/7, the small reduction in power use could potentially make a difference. Finally, active PFC models can handle voltage fluctuations better than their passive PFC models and also remove the need for 110/220V switching, something rarely important, but worth noting. At the end of the day, the improved efficiency and the environmental benefit from Active PFC makes it a worthwhile investment for $10.

That said, SilenX.com does believe in their lower-end PSUs are were fully confident that their 400W PSU passive PFC would be capable of driving even our a high-performance system in our challenging test environments.

Before I move on to the next point, it's worth noting that SilenX.com is currently fighting a battle against Ahanix, ExoticPC, and ColorCase who are also selling "SilenX" power supplies. The only SilenX PSUs that we have experience with are those sold through only.