Hold-up time is one of these things (besides long full-load life) that separates cream from crop in power supplies. High-grade ATX power supplies don't just promise 25+ ms hold up time, but actually deliver.
Some better review outlets test for that, since you can't rely on PSUs actually managing the spec-required 17 ms (I think that's the number, something in that ballpark)
Which reviewers do that?
Two come to mind immediately: https://www.tomshardware.com/ does. German magazine c't at least did, haven't looked at their reviews recently.
http://www.jonnyguru.com/ Has always done some pretty in-depth electrical profiling of PSUs. I usually check them when I need to buy one.
Tweakpc, hardwareluxx, c't, computerbase and probably a few more all use pretty high end ATE (Chroma loads and such) for their PSU tests as well.
c't still does very in depth testing like that when they do a larger PSU lineup test, though not for smaller individual tests.