comments:
alexforencich posted on r/fpga28w
The keying on these connectors can be a bit weird, particularly because of the PCIe 2x3 and 2x4 connectors. I'm actually not sure offhand about the keying. What I do know is that some of the PCIe power extension cables seem to have more flexible keying, and for a couple of boards that I have they really only work worth one of these extension cables attached. These are the specific ones that I got: https://a.co/d/38nm8mu