A bit sardonic, but if peak power is the problem, your PSU better be shutting off, since the alternative is that it'll catch fire at some point. (And it normally will shut off, since it has thermal protections. Those are boolean, not somehow lowering output power.)

And again, the ATX PSU doesn't really matter here, the M/B VRM does. Even if the ATX PSU has a failure mode where it delivers 10V instead of 12V — you can still make 1.05V out of 10V. Decoupling is spread all the way too, so short peaks don't explain a lot either.

Lastly, it's of course possible the VRM is misdesigned. But this issue is seen across mainboards from at least 3 vendors… what is the likelihood of all of them getting it wrong in a very similar way? The primary way for that to happen is if they are all implementing Intel's reference design, in which case it's Intel's fault again anyway and we've looped back to the origin of the discussion…