What you have doesn't use a lot of power. You have a 65W CPU and the 7770 uses less then 100W. (80 something I think.) Your total power draw would be 200W or less.
That said, whoever suggested you buy a diablotek PSU wasn't giving you good advice. I have yet to see a single PSU from them survive any real testing. As such I don't suggest people use them. Return if possible and get a better one. The Antec 380W green or the Corsair CX430 should power that setup just fine. The 7770 just doesn't use a lot of power.