My buddy has a lower end PSU from his older computer he's trying to run an HD 5770 with. It's an Alienware 420W with the specs saying +12V1 has 15A and +12V2 with 18A. Do those two combine to give him his total or how does it work? The power requirements for the HD 5770 is "450 Watt or greater power supply with one 75W 6-pin PCI ExpressÂ® power connectors recommended". I read somewhere that you need at least 40amps so would this work? He's getting low FPS and I don't know if this is the problem. Thank you for your help ahead of time.