620 watt? What? You are better with at least a 750 watt PSU otherwise you are gonna get a big drain on power resources for the GPU and the other components.
Unless you are running Vista or a lower OS, you do need a decent PSU especially for things like video. PC games etc otherwise, if you are just using the PC for typing out your auto biography then the 620 watt PSU is good to go.
Stop posting this. A system like this only needs a 500w power supply..