Not a reliable brand of power supplies. I suggest either one of these instead:
Antec TRUEPOWERII TPII-480 ATX12V 480W Power Supply 115/230 V UL, TUV, CB, FCC CLASS B, CUL - Retail
Antec True Power Trio TP3-550 ATX12V 550W Power Supply with Three 12V Rails 100 - 240 V UL, CUL, FCC, TÜV, CE, C-tick, CCC, CB - Retail
Well I don't think it's laggy because of the power supply. Maybe it's a video card driver issue, or more ram needed.