Corsair AX860

Hi I have a problem that I think the PSU is falling down when just putting

1X R9 280 GPU with a 4790K overclocked to 4.8GHz.



I only have 7 Scythe Gentle Typhoon fans and a D5 pump plus 2XSSD drives.



When I go to run real bench it fails cuts out and reboots but when I put a lower rated GPU in then I have no problem it will run all day on the real bench tests.



How will I test to see if the PSU is not giving out what it should during the tests?



This has been a problem I thought the motherboard couldn't hold the overclock so I now have a new different motherboard also run a 4770K same results only when I put the R9 280 in does it crash when testing CPU stability, the R9 280 is the most powerful GPU I have so I can't try a different one, although I have many other lower wattage GPU's.



I have a multimeter but I don't know how to find out if the PSU is putting out enough and that it is not a PSU problem.



Thanks guys.

Corsair AX860