i am gonna address the gfx card related bits (for psu related info, ask in the psu section).
6550d is amd llano cpu's integrated gpu. it uses pc's ram for video memory. if you have 8gb and then the integrated gpu will use some of it.
you can run softwares like techpowerup's gpu-z
or piriform's speccy
to check your detailed system information.
with gtx 560ti you would be able to play bf3 at settings much higher than you could with the integrated gpu.
bf3 performance analysis:http://www.tomshardware.com/reviews/battlefield-3-graphics-performance,3063.html
a good 550+ watts, 80+ rated psu should suffice.