I have bad experience using M2 adapters - tried to power them and it basically smoked and burnt the 4-pin adapter that was provided - that 4-pin molex adapter is of very low quality.
It wasn't by chance this model was it?
https://minerparts.com/product/pcie-4x-to-ngff-m-2-adapter-with-4-pin-power-cable/I got a couple of those on order to use with Asus PRIME Z270-A (7 PCIe slots) boards, so that I can run 8x 1080Tis per rig.
If the issue is just the 4-pin adapter provided, perhaps I can custom solder (been swinging an iron for 20+ years) my own cable (each rig is going to be powered by a Delta 2400W PSU). So I'd take one of the 32 6 pin to 6+2 pin cables that comes with the REV2-Ultimate kits, and replace the 6+2 pin connector with a 4 pin floppy connector, no?
You can put the iron away and don't worry about those 4-pin molex power adapters. They go straight to the trash bin. At least in my experience with a dozen of Z270-A and Z270E boards and powered PCIe risers, you don't need to provide any power to the M.2 interposer card at all.
Just make sure you fit it in the slot correctly so it does not shift sideways. Some (most) of the cheap interposer boards I've seen had PCB routing done way out of spec with the key gap being too wide.
-scsi