[AChimp]

Power supplies that come with the cases are notoriously bad for being low quality (unless you're buying a super expensive case). I mean, if a case and power supply combo is $50, and good power supplies cost $50 by themselves, how good is the one that comes with the case? Most of the time the power supplies provided with the case aren't even capable of outputting the advertised wattage for long periods of time, which is why people start running into problems when they begin to upgrade their machines with newer hardware.

Unless you are running a super fast processor, CD/DVD burners and the latest video card (and don't plan on adding much more stuff) you can probably use a 350- or 400-watt power supply and be fine.