For every rule about powerline networking, there is an exception.
When I first moved in here, I used some surplus powerline adapters I had lying around to connect my machine, my HTPC, any other computers and devices, and the laptop which was at that point slaving internet to the rest of us. As holes got drilled and cable was run, each PLA was retired until there are only three. One is in my computer room, connected to the LAN. One is connected to the HTPC, which is in a very awkward place to run a proper hardline to. The third is on another wall, feeding my downstairs WAP.
How is this interesting, you ask? Well, the HTPC and my computer room are on different legs.
And the wall with the WAP is on a WHOLE OTHER METER. Had our power turned off late summer over a billing error. My whole downstairs was dark, except for the WAP. Turns out that is accidentally wired into the upstairs supply, which is no way connected to the downstairs.
Best I can tell, the nearest shared copper is out at the street, on the pole. Even so, it works. PLAs are part of the Old Dark Magic, not to be trifled with.
I've been here long enough that I think I can forgo a signature.