Anyway, just so I can close this thread, the Oculink to M.2 adapters I had did not have any power input, and my current mobo does not provide power via Oculink (there may be mobos that do though!). In the end, I chose to go the U.2 route: Oculink → powered Oculink to U.2 cable → U.2 to M.2 adapter, and that works a treat. I also tried a powered Oculink to M.2 adapter, but it blew out one of its capacitors just as soon as I turned on the box, so I just gave up. The U.2 detour is good enough for me.