if you use a power calculator...
388w minimum power required however you need to step up the size a bit so you are only using about 80% capacity.
you should buy a 500w psu however a 550w would be better.
buying a 650w would allow you to upgrade to a better gpu later on and allow you some overclocking headroom. if you do not plan on doing this then you dont need to buy a 650w psu.
buy a seasonic psu. or xfx (since they are made by seasonic). pc power & cooling isnt a bad brand either.