Hodgkinson
if this can "help" you, i can say that even some pricey PSUs acts very weirdly when used on our amigas.
I'm just "fighting" with the n° PSU (Seasonic 400 w) purchased brand new from RS.
These PSU are designed for a (no need to say to you) crap power demanding by GFX card on the 12v rail and above all, they have a totally unused by us, 3.3 volts rail that summed on some "hidden" sense wires, lands in a totally screwed/unbalanced power balancement.
In few word, i have 4.90 volts (on the +5 v rail) and 12.47v on the 12 volts one. (the funny thing is that i have 3.300 volts on the 3.3 rail perfectly stable even with a low load ...lol!!!) and all this in a quite loaded A4000 in a PowerTower.
I've fortunately found a way to re-route the fisking mis behaviour that i'll let you know, as soon as finished (my oscilloscope is under repairs .. hugh!)
Sorry for the demiOT :-)
