I agree, it's very, very doubtful that it's a power supply issue, however, for the sake of accuracy, let's have an understanding that neither the model nor the age of any power supply in question has any bearing on whether or not there COULD be a power supply issue. I've seen brand new out of the box Seasonic Titanium Ultra 850w units, among a LOT of other very good units, have issues from day one. So, it CAN still be a power supply issue, in ANY case where there is EVER a problem on ANY system, but I'd agree that it's a lot less likely than your four year old motherboard which is what I wanted to initially go after anyhow but I always have to ask about the power supply because we see SO many issues that are power supply related here, and in our daily workings, that at first wouldn't seem to be related.
Energy saving features have little to nothing to do with an overclock causing issues that removing the overclock resolves. It's a lot more likely to be related to an inherent problem on the board on the interconnect between the PCI circuit and power regulation components, or possibly just the power regulation components (VRMs) themselves. Could also be a capacitor issue, so visually check for any bulging or leaking capacitors. There won't always be visual evidence, but often there will be.
As I mentioned earlier, when those Z97 Krait boards first came out, I and I'm sure others as well, saw an unusually high number of them with problems on this forum, and none of them seemed to be exactly the same, but they were all issues that a replacement or different board seemed to resolve, so the assumption would be something sub-par in the quality control or inherent design of that specific model on that specific chipset, as I have not seen the same problem on any other Gen or chipset version when it comes to the Krait model boards.
And it may not be related to the model at all. It may simply be a defect in general or fatigue due to the age of the board and the fact that it's been riding an overclock for a while now when it wasn't a particularly great overclocking board to start with.