The OP should calculate the loads like this overclocked example. All 12v currents, it's all that really matters with an AMD64 system. Your not going to bother the 3.3V/5V rails for much tbh.
Opteron 170 @ 2.8GHz 1.5v = 190w (Stock 110w)
Motherboard approx ~ 45w
X1900XTX say 700/850 = 145w (95% is 12v)
X1900XTCF = 107w second card isn't running flat out, say max 75% of first.
Xfi ~ 8w
2 Raptors (0.35mA @ 12v sustained, but startup goes way higher maybe
2A ) = 48w at spin up, 8.4w at load.
2 SATA 7200 RPM (0.5mA @ 12v, 1.8A at startup) = 44w start up, 12w at load
1 optical drive system = 17w
1 FDD = 5w
3 x 92mm fans ~ 36w
2 usb devices ~ 5w
What's that just using generic values? 55A/650w all on the 12v. If everything started at once and went to full load
![Eek! :eek: :eek:](/styles/default/xenforo/vbSmilies/Normal/eek.gif)
Which of course they don't. Take the hard drives at the sustained read/write values, not the spin up and that's 48A/580W (12V) still not quite right. For power calculations its normal to include factors for diversity (i.e not everything runs flat out all together), loss (inc derating) and efficiency. I usually work on stuff a bit bigger than a PC, but say the running load is only 80% of maximum, but the losses to heat and resistance are 5% and the PSU is down 5% from age (or its not a review sample). At a conservative estimate say you need 90% of the maximum load 43A/520w at 12v. And remember that's now a constant sustained load, not a millisecond peak value. Watch it, because some firms like to quote peak or they rate the unit in a freezer. Look for the ones rated at 50C, PSU's derate very quickly, like 10W/C or -100W for a delta of 10C and so on.
That's still quite a load, more than a lot of PSU can handle. You don't need 25A on all rails, 12V2 is supposed to be for the CPU only in ATX, that's going to need 16A. Some of the newer PSU's like the FSP
FX700-GLN will be able to handle it. £103 (inc) with 4 rails and 50A/600w (12V) And the PCI-e are connected to different rails so they can't reach the 240VA limit.
FX700-GLN
12V1 - CPU 1
12V2 - CPU 2, PCIe 2
12V3 - Motherboard, SATA, 4-pin molex
12V4 - PCIe 1
Still if you can afford £300/£350 for the 850w/1kW PCP&C, I would, they are the best.