im using a 550W coolermaster PSU
if it is a coolermaster extreme power plus 550w psu, you should upgrade to a better psu like corsair builder cx 500 v2 or seasonic s12ii 520w or antec neo eco 520c. then get a gfx card like geforce gtx 560ti / 560ti-448 cores or higher or amd's radeon hd 6870/6950 or higher. bf3 loves using video memory so aim for a t least 1 gb gfx card, 2gb would be better. you can consult this article on how different gfx cards perform on bf3 (single player).http://www.tomshardware.com/reviews/battlefield-3-graphics-performance,3063.html
multiplayer would require more powerful cpu. you could oc your cpu with a good cpu cooler to improve mp performance.