NEVER cheap out when it comes to your power supply!!!
As all generic, no name, PSU vendors tend to grossly overstate the power rating of the crap they sell, I advise you not to buy a no name PSU. Besides they are not reliable and can fry your system components when they fail or have power spikes.
The PSU is basically the engine that drives you whole computer system.
Only buy an 80 plus certified PSU, from a reliable brand name such as Thermaltake, Enermax, Cooler Master, Antec, OCZ, or Corsair.
Also a modular PSU is preferred, as it allows you to only use the power cables you actually need.
This will eliminate cable clutter, and allow for better air flow inside your box. It means a more proper cooling result for your system.
Last but not least, it's always best to have a full ATX size PC case with bottom PSU mounting, for many reasons.
Top reasons being better air flow in the box and less vibrations and noise.