Here's how it goes:
Network router on one side of the house w/ my main office and power line connected on that end.
On the other side of the house, my laptop, plugged into the powerline on this end. However, there is a tall light that I use for my room that is plugged into the wall. Now:
If the light is plugged in but NOT on, the power line networking does not work.
If the light is not plugged in, the power line networking works.
If the light is plugged in but ON, the power line networking works.
I'm not electrician nor do I know much about the details about how power line networking works, but why exactly does the thing work and not work in those instances that I have listed up there? Btw, I've tried this many many many times over so it's not a fluke or anything.
And just to add .. I would do wireless networking but the distance is way too far for the signal to reach and the signal boosters and repeaters that I tried don't play well with 128bit encryption.