Originally Posted by Schoenfeld
This is utter nonsense. Do you have a towered A1200 with a 25-Zorro-slot expansion, fully equipped with power-hungry cards?
An A1200 board takes 1.7A on 5V while booting, and 1.5A when idle.
ACA1231 takes 0.56A under full load, 0.45A when idle
Indivision AGA MK2 takes 0.45A on highest output pixelclock and DVI enabled
What do you do with the spare 12 amps?
ATX PSUs are not the proper choice for an Amiga, because they rely on point-of-load regulation inside the supplied computer. It was way before the ATX standard that the 5V rail was used inside the computer without further regulation (back when the Amiga was new and PCs used the power supplies with P8/P9 connectors). Nowadays, the 5V rail is not critical any more, so regulation is not sufficient any more.
The old P8/P9 PSUs are too old to still supply low-ripple power in the year 2012. I must admit that the only way is currently to refurbish the original A1200 PSU with new electrolytic caps, but this should only be done by a professinoal - the primary side of a PSU contains voltages that are way too dangerous to be handled by a hobbyist (no matter how experienced).
Strange, then I do not know why my Amiga wont boot of the 10A PSU, worked until I put the indivision in then I could not get it to boot, it froze and behaved strange just before the AmigaOS was loaded fully, replaced the PSU with a stronger one and bam worked.