How did you come to the 550W figure? According to https://www.asus.com/Graphics_Cards/MATRIXR9280XP3GD5/#specifications each card needs 300W.
Then you also need to factor in the power used by the rest of the machine.
Then add a factor of say 20% to accommodate spikes in power draw.
I'd look at something with 700 - 800 watts and 80plus certification. Stick to the big brands. Wattage isn't actually the best measure... taken from http://www.extreme.outervision.com/PSUEngine
The recommended total Power Supply Wattage gives you a general idea on what to look for BUT it is NOT a crucial factor in power supply selection! Total Amperage Available on the +12V Rail(s) is the most important, followed by the +5V amperage and then the +3.3V amperage
Then you also need to factor in the power used by the rest of the machine.
Then add a factor of say 20% to accommodate spikes in power draw.
I'd look at something with 700 - 800 watts and 80plus certification. Stick to the big brands. Wattage isn't actually the best measure... taken from http://www.extreme.outervision.com/PSUEngine
The recommended total Power Supply Wattage gives you a general idea on what to look for BUT it is NOT a crucial factor in power supply selection! Total Amperage Available on the +12V Rail(s) is the most important, followed by the +5V amperage and then the +3.3V amperage
Thanks for reply.
I'm using a kill-a-wattmeter, the MAX it has used is 550w inc MB. I just want to run 2 cards off the MB/PSU.
So add 20% to 550w = 660w, so a 700/750w 80plus will be ok.
Think i will get this -
http://www.dabs.com/products/coolermaster-700w-g-series-g700w-80--bronze-power-supply-8Z2S.html?refs=394900000&src=3
