This was a misinterpretation of ATI's suggested PSU sizes for an entire system that keeps getting repeated. The math just doesn't work.
40 amps x 12 volts = 480 watts. http://www.amd.com/us/products/desktop/graphics/ati-radeon-hd-5000/hd-5770/Pages/ati-radeon-hd-5770-system-requirements.aspx450 Watt or greater power supply with one 75W 6-pin PCI Express® power connectors recommended (600 Watt and two 6-pin connectors for ATI CrossFireX™ technology in dual mode)
So how could ATI say your entire system could run conservatively on 450 watts when the GFX card was pulling 480 ???
You can do the math yourself here:http://www.antec.outervision.com/PSUEngine
the 5770 works out to a peak 119 watts or just under 10 amps.