There are classic home automation systems like x10 that potentially predate wifi and offer wired solutions that use the power lines themselves for wired communication, you might want to check these out
I've heard that a lot of these systems that transmit data over power lines have a tendency to trip the arc-fault breakers that are required in a lot of new construction.
I remember playing with x10 consumer devices I bought off the shelf from radio shack 25 years ago. The tech was slow but very functional even back then.
Powerline Gigabit Ethernet is a thing, but it's bordering on wireless (uses the power wiring as a "guideline" as to where its RF energy should go). This makes the network attachment unit costly and adoption low. For most applications WiFi is cheaper and more convenient. Anyone who wants really solid connectivity will lay Cat5.
The use case here is turning an outlet or light on/off, so latency matters, but it requires nearly zero bandwidth (assuming that you're not talking tcp). Granted, x10 security cameras exist.
x10 speaks a protocol designed for this purpose and requires a base station.