Lol, your motherboard does not consume 350 watts of power. Your motherboard itself consumes very, very little power. A very high end CPU might hit the 150W range (not overclocked) and an extremely powerful video card might hit 100W (again, not overclocked, no SLI or CrossFire or other multiple card configuration). Hard drives will consume a maximum of about 25W apiece, though they are getting lower with green tech being hyped (SSD drives are much lower in most circumstances). Optical drives consume more power at peak load, but almost nothing when idle, so I usually exclude them from calculation (your CPU will almost never be peaking at the same time as your optical drive). That just leaves memory, PCI devices, and USB/other external peripherals, all of which contribute minimal amounts.
If you want a good calculator that has results very close to my own calculations, try
Thermaltake's. Most of the hype regarding wanting a 'more poweful' PSU is drawn from a trend of poor quality PSUs 5-10 years ago when barebone machines were popular. Because these PSUs were of low quality, they did not handle peaking very well (booting your computer is actually a peak time since voltage regulation logic has not yet initialized) and therefore gave the impression that the user needed a higher power PSU. In this circumstance you actually need a higher
quality PSU. I'd take a $90 400W Thermaltake over a $50 600W no-name PSU any day.
