Don't really have the money at the minute, so I was hoping that it would be stable enough so that I wouldn't have to get a 600w. So could it keep the R9 280x stable?
It really depends on the wattage you have on your twelve volt rail of your power supply. So find out what the minimum wattage you need to run the card should be on the box somewhere. Then find out how many watts is on the 12 volt rail of your power supply. If the wattage of your power supply is close you should be fine. Video card manufacturers always overshoot the power requirements because plebs buy crappy psu's and then complain that it doesn't work. So if you bought a decent PSU even though it is only 600watts you should be okay. Also the worst that could happen if you're wrong is your computer will shut off in the middle of a graphics heavy scene on a game you're playing and then you'll know you need a better PSU.
Power Supply:XFX 550W 80+ Bronze Certified ATX Power Supply (£46.36 @ Amazon UK) Total: £46.36 Prices include shipping, taxes, and discounts when available Generated by PCPartPicker 2014-09-22 21:24 BST+0100
Hey , i was wondering the same kinda thing a few days ago i am running an fx8350 @4.82 Ghz and an r9 290x with a small cx600 watt psu and i was quite worried so i went to the hardware store and bought a power meter that goes on the plug of the pc ... so i started playing watch dogs on ultra everything and 8x msaa and the computer didnt use more than 460 watts for 2 hours ...
So id say you fine as long as ur psu is a good name