I have been experimenting with a ZyXel PLA-407 Powerline Pass-Thru Ethernet Adapter. Per the instruction manual, it “supports a data transfer rate of up to 200 Mbps.” Like most people, I get a fraction of this at best.
Approximately 80 feet of 12 AWG 3-strand copper wiring connects the two powerline pass-thru ethernet adapters. On the first test, I was able to achieve a maximum sustained throughput of approximately 15 Mbps. I wondered if both electrical outlets were on the same phase. They were apparently not on the same phase. I swapped the breakers of my endpoints to be on the same phase and ran the test again. The maximum sustained throughput doubled to approximately 30 Mbps! Definitely an improvement, but still pretty weak compared to WiFi.
Amazon reviewers seem to have the same experience with other brands of powerline pass-thru adapters—review after review stating that the actual bandwidth falls short of the advertisement, so I guess the problem has more to do with the standard than the manufacturer. Despite the weak bandwidth, I am satisfied with the purchase. It was $50 for the pair, and even though 30 Mbps is not great, it is still working better for me than WiFi was through three walls.