So, I finally got my hands on a Kill-A-Watt, and I'm convinced that the "need" for high rated power supplies is a scam. System: i5-3570k, 4.5 ghz, 1.28V Gigabyte GA-Z77X-D3H Patriot Viper DDR3 1600 16GB, 1.5V (stock) Visiontek 7970 Ghz, 1125/1600, 1.3V (stock) Intel 330 160GB SSD Seagate Barracuda 1.5 TB Green 2x 220mm Fans 2x 120mm Fans DVD Drive OCZ EliteXStream 800W Power readings from the Kill-A-Watt: Idle: ~80-90W Normal Usage: ~130W Prime95: ~190W Heaven DX11, Full Settings: ~280-320W Heaven Dx11, Full Settings, 7970 @ 1.38V: ~380W Extrapolating from a review Anandtech did: That means that with it never dips below 82% efficiency at the ranges I'm running other than idle. To adjust: Normal Usage: ~107W Prime95: ~155W Heaven DX11, Full Settings: ~230-262.4W Heaven Dx11, Full Settings, 7970 @ 1.38V: ~311W This is a mildly overclocked system with a large card. At worst, I was delivering 311W to the components. That means a 430W would be able to handle this load, and I might even get away with xfire/sli at 500W, given enough connectors (the 7970 at load only used up another 200W at full OC, and around 100W with a normal OC). It seems to me like our PSUs are grossly overrated for their jobs.