The mother does not work with a working power supply, what could be the problem?

Question

Power Supply

There is a Gigabyte GA-EP43-UD3L mother, there is an ATX 550W Corsair power supply. And they don't get along with each other. I will make a reservation in advance that both the mother and the BP are serviceable. The mother was on diagnostics, BP works great with any other mothers.
And the trick is that when you insert 24 + 4pin into the mother, when he just entered the middle, the indicator on the mother lights up, in general, it shows signs of life. And then, when you insert normally - zero reaction. That is, simply put, not a damn thing works).
Tried this block with another mother - everything is fine. Another one is the same. This one is a problem. With another power supply, though with 24pin, it works, but with that it doesn’t work.
What can be the problem?

Answer 1

the same problem, xs anyway, I'll go to the store tomorrow to figure it out

Answer 2

I have been using motherboards from this manufacturer for many years, I have never had any problems. It is enough to check the power supply by simply closing a pair of wires (green and black) with a piece of cable, it turns on, it means alive. It is not more difficult to check the mother, most likely there are active USBs that supply voltage in the off mode of the power supply (the indicator lights up). The second option is to check the pinout of the front panel and the power connector for contacts, if everything works here, then most likely some kind of incompatibility magic is involved))).