300 Watt power supply graphics card and Battlefield 3

tell me the brand of the psu and your pc specs

seeing that you would like to play battlefield 3 with a 300 Wat psu is pretty low.

I google some cards and looked at manufactures websites, ( Nvidia, Ati ). If you would like to play Battlefield3 (Bf3) i suggest you would upgrade the psu no matter what is in the system. Just so the power supply is not being stressed to overload.

i have a compaq CQ3020IL branded PC which i upgraded the RAM to 3GB and i've put an ATI radeon X1550 PCI-E graphics card to it.... do i need to upgrade my PSU if i want to play battlefield 3 . if yes then what PSU should i get and i am also planning to replace my older card wid an ASUS GTX 550 ti card. what will be the cost of replacing my PSU?

Depends on where you live. on newegg you can get Antec EarthWatts 500w for $50:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

That power supply is a quality unit, it won't disappoint you.

Just a note: don't buy just any power supply, look at the brand. Quality brands are Corsair, Antec, Seasonic, XFX. If you buy a cheap generic power supply, it might fry your system!