This is a very fresh find 8/2026.
ATX 3.1 this is computer power supply pack of specifications, an product design standard, according to INTEL requirements.
Every such a pack of electrical specifications this includes PASS-FAIL limits, under Low load tests, and under High load tests per rail.
Naturally, if you get the ATX 3.1 documentation, and read all pages, eventually you will also become aware of all details.
My discovery this is a fastest way. 
From video footage, of Asian factory this be ATX PSU manufacturer, I did steal two screen shots.
a) The Low current stress test, this is used for measuring upper voltage per rail.
b) The high current stress test, this is used for measuring lower voltage per rail.
What appears as interesting to me, this is the low current stress test, as they applying
500mA as minimum load at all rails.
Why this is of importance ?
Because with ATX 3.1 PSU's, if you try to evaluate voltage per rail over your bench, other than a quality multimeter, you will also need this 500mA loading per rail too.
At high current stress tests, per rail, here everything is related to PSU per rail wattage.
The specific DUT, this is an 750W / 80 Gold / for the USA only.