I want to upgrade my graphic cards

Solution


cooler master is a very good PSU company, you should have no problems using the gt 640 with a 300W cooler master PSU.
Since u have only a 300W PSU... Consider a HD 7750 GDDR5? There is no need to have a 6-pin power conductor for her, your PCI-E port could support.

HIS iCooler H775F1GD Radeon HD 7750 1GB 128-bit GDDR5, $90
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161403,
it's the fastest GPU which doesn't need additional power supply I could find.
 




Just plug your card in, if she works, its OK, no need to worry.
 
thank you, you're awesome :)