It is 100% not an incompatibility...
Please read: https://en.wikipedia.org/wiki/Power_good_signal
I know of the Power Good specification and such. Still, there just are incompatibilitys in the real world - they don't happen that often but they do happen.
ATX spec states how the PSU MUST work, no ifs, maybes, perhaps we should... It states that the power good signal MUST be present after the PSU stabilizes. It never presents the signal, EVER, as such it doesn't matter squat if it works with another motherboard, it is faulty.
That's the theory...
In the real World it's not how it goes...
It's how it should, I agree with that, but it's not the way it is...
If it did work with another motherboard it just means that that other motherboard is also faulty or is some cheap chinese crap that doesn't conform to standards.
No it just means there is an incompatibility...
There are also other factors beside the power good signal, it's not only that. And sometimes you just have problems...
Take a look at the PCB manufactoring tour on this site. Somewhere there was stated that only one particular jelly bean chip (some LM I think it was) did work as intended...
And pls do NOT blame the chinese for that. They do it cheap because we want it to be cheap. They just have a different mentality...
If I did not have the equipment to TEST and PROVE the PSU is providing the voltages as expected, and PROVE that the signal good is MISSING, I might believe you... But... I DO have the equipment consisting of two reputable multi-meters (Agilent and Bryman), a very recently calibrated bench multi-meter (Escort 3146A), and a 1Ghz/s 100Mhz DSO. Are you saying that all my tools are faulty?
Seriously... It is not a matter of the signal is low, or inconsistent, or sporadic, it is simply NEVER, and I mean NEVER presented. Doesn't matter what you say, any 1/2 decent motherboard wont post without the power good signal being presented unless it does not conform to spec, in which case it is a cheap ass load of crap that would never see use in my office.
The fact that if I manually pull the power good signal to 5v standby everything operates as expected, post, boot and rock stable under load, clearly shows your 'guess' at an incompatible power supply is complete and utter bull.
You seem like one of those
idiots people that believe that you need $10,000 nude virgin OFC cables for your digital signals...