The video card is always the big power hog in a system. By itself the 2500K draws 95 watts ( not overclocked ). In fact as long as you have a quality power supply you can run a system with any single graphics card including the $500+ GTX 680 / HD 7970 with a 550w power supply.
Here is a list of power requirements by card. This is for the entire system not just the card.
Quality power supply brands would be Corsair, Seasonic, PC Power and Cooling, XFX, Silverstone, Enermax, OCZ and Antec. Some other brands have good models but these brands are pretty much good across the board.