I have a Huntkey vPower 550W PSU on my desktop powering a Core i3 530 on an Intel DH55TC motherboard with 2 GB DDR3 memory. I am planning to upgrade my memory to 4 GB and add a GT 240 graphics card. Will the existing PSU support this upgrade? I already have two SATA hard drives and am planning to add another one soon. Also, advice me on which maker's GT 240 I should buy.