We conducted an in-depth investigation about power supply units (PSUs) and the problems that you might face when using high end SLI/Crossfire systems. The recent problems we had with single and dual rail PSUs made us look first at the ATX 2.0+ specification.
The essence of the problem actually lies within the big four, Intel, AMD, Nvidia and ATI. They are all guilty for going too far, too fast with power specifications, in order to reach the performance crown, of course. For example, the ATX 2.0 specification requires two 12V power rails or more and some of the manufacturers designed two rail designs at around 20 amperes per rail. The problem is that Intel's Extreme Edition or Athlon FX60 can easily reach that. We learned that Intel's latest Extreme edition draws 22 to 23 amperes of its default 3.73 GHz clock speed. As soon as you overclock the same CPU at 4.4 GHz your CPU will draw as much as 28 to 30 amperes but this number includes all the fans and the pumps that you need to keep the beast cool.
Very knowledgeable engineers confirmed to us that a card such as the Geforce 7800 GTX 512 or Radeon X1900 XTX requires roughly 12 to 15 amperes. Once you plug those cards in SLI/Crossfire mode, they will need twice as much. Once you overload one of the 12V rails, the machine will simply shut down in order to prevent the destruction of your expensive machine.
So, you do the sums - a CPU with up to 30 Amperes plus two cards that need additional 30 amperes will get you to monstrous 60 Amperes. If you don't do a dual rail design you are risking setting your PC on fire, and if it weren't for those safety mechanisms, you could easily see some real fire from your PSU. You could blame Intel for its extreme CPUs, you could blame AMD for its FX 60s - almost as bad with the power consumption, you could blame Nvidia for its SLI that started this whole mess and you could blame ATI who followed Nvidia and made Crossfire.
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