When you're assembling a basic system with or without an entry-level card you don't need more than 300-450 watts to power it. These PCs also benefit from a good and stable PSU, but there's a lot of junk available in this lower segment. We thought that was a good reason to separate the wheat from the chaff, so we put 39 power supplies through our standard testing process.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips