I'm calm ... But I feel something doesn't smell right in your description. How that bad PSUs could turn on a fan (+12V rail), light up LEDs (+5V and +3.3V rails ?) ?
Major question would be the same - did you measure all rails on bad PSUes ?
So far, on three 24-500s, I've heard the HDD spinning and the fan, very briefly, spin and stop. I can see no other way the HDD can get power except from the power supply board. I never said that you see the front panel lit and have a bad PS. If you don't have front panel illumination, it seems to be caused by a bad PS board. A board with more than one output. So, the HDD spins and the fan tries to and the front panel isn't lit up at all. Bad PS.
And no...I didn't measure any voltage and I have no idea what a "rail" is. I keep saying I'm extremely lazy and replacing the PS board and having the HR work properly again is enough for me. It's quick and easy and you need no technical ability other than how to use a Torx wrench and pull connectors apart. Literally a ten minute job once you get the cover off. That's taking your time.
Measure the voltage of a rail....