The short story. I have a Cooler Master Real Power M520 power supply.
My current config:
Mobo: AsRock Z75 Pro3
CPU: Intel Core i5 3570k (not overclocked, but I'm asking your opinion what would happen if I go for about 4Ghz)
VGA: Sapphire Radeon HD 5770 Vapor-X
RAM: 2x4GB Corsair DDR3
HDD: 1 Sata
USB powered gaming kayboard, mouse and headset, XBox 360 controller reciever.
The main question is that would I be able to install another HD 5770 and run fine with the 520w power supply. Based on this website (http://www.extreme.outervision.com/PSUEngine) I need a 400w PSU. The CM's website says this PSU can give 600W at top, 520w continously.
For a system using two Radeon HD 5770 graphics cards in 2-way CrossFireX mode AMD specifies a minimum of an 600 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 32 Amps or greater and have at least two 6-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most critical factor.
Overclocking of the CPU and/or GPU(s) will require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock being attempted.
The Cooler Master Real Power M520 (RS-520-ASAA-A1), with its maximum combined +12 Volt continuous current rating of 34 Amps and with two 6-pin or one 6-pin and one (6+2)-pin PCI Express supplementary power connectors, is sufficient to power your system configuration with two Radeon HD 5770 graphics cards in 2-way CrossFireX mode.