Power SATA hat form external PSU

Hey guys,

I’m just planning a PCB as a connection between my RPi4b and the Quad SATA hat since both PCBs - RPi and SATA - should be horizontally parallel mounted on a PCI bracket / frame (the right PCB is the SATA hat, the grey block represents the SATA sockets with the minimum height for plugged in SATA cables).

Now my problem is the power supply. I’m having a 12 V PSU with a barrel jack plug (5.5x2.5mm) which fits perfectly in the socket on the SATA hat but I can’t use this socket since there won’t be any space for that (it’s right next to the RPi’s GPIO header).
So I thought of connecting the barrel jack plug to a socket on my own PCB and connect this to the 4 pin ATX PSU socket on the SATA PCB.

For a test I just connected 12 V (and GND) from another PSU to the ATX PSU socket. When powering the PSU, the green Power LED on the SATA hat flashes once for a split second and turns off afterwards. Neither the connected 5 V CPU fan is powered.
The ATX PSU socket is labeled with 12V, GND, GND and NC / NC 1 or something similar. I assume this means 5 V - is this correct?

My question is: Do I need to deliver both, 12 V AND 5 V via the ATX PSU socket / why is delivering 12 V with the barrel jack enough while it seems not to be via the ATX PSU socket? There’s no current flowing, the test PSU “delivered” 12V@0A…

I hope someone has any idea why the board won’t “turn on” properly.

Many thanks in advance!

I solved the problem… I limited the test PSU to 100 mA maximum. After increasing this limit to 500 mA, the board (and RPi) was powered properly.