What brand and model is the atx psu's you have tried?
So wanting to replace my old and trusty original A4000 PSU with A4000 ATX PSU power adapter
I purchased a micor-ATX psu that fits nicely into the A4000 PSU chasis BUT....
1-tried connecting micro-ATX and nothing..PSU not starting at all nor A4000 so tried another dull size ATX PSU and same thing
2- contacted Amigakit and they told me it was some 'sense' thing with newer PSU's but I had my suspicions
3- tried starting the PSU without connecting to A4000 and voila PSU started up no problem with following voltage readings:
Grey (what you call purple)-+5.21v
Do you mean that the cable from the ATX PSU is grey and the cable on the adapter is purple?
Purple on the ATX connector is 5v vsb and that would confuse the heck out of your amiga, since it would get pwr_good signal and no voltages as soon as you flip the powerswitch on the back of the atx psu.
this is way low, the psu probably regulates from the 3.3 rail...
4- let Amigakit know and they said these readings were fine and adapter was working ok but offered no help as to why it wasn't powering on my A4000
The adapter might be technically working buut these readings arn't "fine"
I really hate when you are expected to be an electrical engineer just because you have an amiga
I do have an amigakit atx to a4k adapter cable I haven't had time to test it, but it seems to be correctly wired ( i do wish it connected all voltage cables and not just one single) but I have experienced atx psu problems with a hacked square din atx cable.
When I initially made it I used a diffrent psu, and ran into problem because the newer was expecting 3.3 load.
Amiga HW goes insane in the membranes if it does not get more than 4.75v :p