This is a shelf designed to hold a Google Wifi router. So that it has a place to live in places where you don't have any furniture to put it on (e.g. a corridor).
It is installed between the wall and the socket plate thanks to the existing socket screws. BEFORE installing, make sure you've switched off the mains power to the socket.
This was designed for MK single sockets (round angles at the bottom).
The fixing centres for the screws are standard for all single sockets, so you should be able to install this shelf on any single socket.
Make sure you have a good infill setting (+40%) as it will increase the strength of the shelf.