Power Line adapters are horrible and ancient completely obsolete technology. Just like you stated technically they do work but all the interference on the power lines causes the connection to be ridiculously slow. Power Line adapters were very good when people had 56K modem speed to the home.
Use either a wired connection or a wireless repeater both of which are much better and also significantly cheaper than the Power Line adapters.
TheTick (aka "Moose Twit" affectionately called by chht)
Roku 3 for Pokémon TV / YouTube / Animal Planet GO / HBO GO. Chromecast for most other media because Roku Mirroring sucks , how many clicks in Wndows 10 (about a dozen) to Miracast on Roku vs 2 with Chromecast.
Verizon FIOS TV and Internet Service