Alright so I purchased a pre-built computer from BestBuy back in August and I want to get a new graphics card to replace the current one which is a Nvidia GT 530. I understand I have to get an appropriate power supply as well. The card I would like to get is a SAPPHIRE 100283-3L Radeon HD 5770 1GB. The computer I currently have is an Asus CM6850-07. What kind of power supply should I get that I wont have problems with and will the Radeon 5770 work with my computer? Please Help, Thanks.