Why is my performance low on a bfg gtx 260 oc?

i noticed a slight performance boost from the video card i once had but i suspected higher frames per second and then i noticed that it was on power saver 3d is it because my power supply is to weak?it is a rocketfish 500 watts if it is would a Coolmax CU-700B 700 Watt ATX EPS/12V Modular Power Supply do the job????