Q: if i have a 700w computer power supply, does it always automatically consume 700 watts or does it only consume the amount which my pc uses up?
A: no the power supply only outputs as much power as is needed. here, read this: http://www.extremetech.com/article2/0,1697,1938044,00.asp specifically this part, "At first blush, you might think that an 850W power supply would consume tons of power, but that's not necessarily so. Modern power supplies deliver power only when requested."