@Tom you can refer this:

hope it helps.

Although not concealable in a wall, I needed a quick solution for a four way trailing socket.

I used this PSU enclosure:

Along with a NodeMCU, 16A relay and a transformer from a mobile phone charger (£1) I just mounted them in the plug and wired the trailing socket to the relay. I also include a TMP36 Temperature Sensor inside just in case anything got too hot and I would get a nice early warning.

Worked like a dream and has been rock solid ever since.