For a system using two GeForce GTX 480 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 900 Watt or greater power supply that has a combined +12 Volt continuous current rating of 67 Amps or greater and that has at least two 6-pin and two 8-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important.
Since you never specified the Corsair 650W modular power supply model:
The Corsair Enthusiast Series Modular TX650M (CMPSU-650TXM), with its +12 Volt continuous current rating of 54 Amps and with two (6+2)-pin PCI Express supplementary power connectors, is insufficient to power your system configuration with two GeForce GTX 480 in 2-way SLI mode.
The Corsair Professional Series HX650W (CMPSU-650HX), with its +12 Volt continuous current rating of 52 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is insufficient to power your system configuration with a single GeForce GTX 480 in 2-way SLI mode.
The Corsair Professional Series Gold AX650 (CMPSU-650AX), with its +12 Volt continuous current rating of 54 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is insufficient to power your system configuration with a single GeForce GTX 480 in 2-way SLI mode.
The Corsair Enthusiast Series Modular TX850M, Corsair Professional Series HX850W (CMPSU-850HX) and Corsair Professional Series Gold AX850 (CMPSU-850AX), with their +12 Volt continuous current rating of 70 Amps and at least four or more (6+2)-pin PCI Express supplementary power connectors, is the lowest capacity Corsair modular power supplies that meet the power supply requirements if you're not planning on overclocking the CPU and/or GPUs.