i current have an acer aspire everything is stock hardware apart from my graphics card. my cpu is amd phenom quad core 9550
GPU is ati radeon 4870 dual sonic edition.
my PSU is a stock Sparkle FSP400-60THA-B/THA-B204 400W ATX12V 2.0
my problem is that i just wanna create a decent gaming rig and atm im having trouble on wat part i should change in my pc as i get noticeable lag on steam with a really old game
the only game i can run full spec smoothly is grand theft auto san andreas. do i need a better power suply please write specificly and detailed