Mod Extreme Pro 700W causing crashes?

Recently upgraded to the rig under my avatar.
Seem to be having problems with the GTX 970 with regular crashes, sometimes just a blackscreen, forcing me to manually restart, sometimes a blackscreen and automatic restart, sometimes a pale blue screen with a manual restart required.
This system is currently running flawlessly with the previous HD7950 installed and the GTX970 is being returned after an RMA, the suppliers state 'no faults found'.
Currently (pun intended) it's running off a OCZ Mod Extreme Pro 700W purchased in 2010, Reviews of the Maxwell cards show they're very demanding of the PSU and I'm wondering if a change is in order or if underclocking would further indicate the PSU is, indeed the issue.
 
Cheers, Bruce.
Looks like we agree, I knew the current PSU wasn't the best available when purchased and your views and those in the review only reinforce my original thoughts: Probably time to change it.
Oh well...Yet more expense, still, at least I can drop it into my brothers Frankenstein i5 750 offcast.