This may seem like a really stupid question to many of you, I've tried reading about it but still cant seem to grasp the concept. If I have one GPU that needs at least 450 Watts to run correctly, and I want to add another in SLI. Does that mean I need a Power Supply of at least 900 Watts? I've scene people run tandom SLI with like 600-750 Watt PSU? Is a 450 PSU generating a constant 450 Watts? Could someone explain the relationship between power generated by a PSU and the Wattage needed by system components?