The brand/quality of the power supply is very important, some cheaper models do no output the posted power. Take a look at this link and choose one that is tier 1, 2A, or 2B. If you are on a super tight budget and cannot find any in those tiers then look at the tier 3.
This is one of the best options for a tier 2 PSU and would be able to power your system easily. Power Supply:XFX 550W 80+ Bronze Certified ATX Power Supply ($49.99 @ NCIX US) Total: $49.99