plug (something) in
Definition: to connect a machine to an electricity supply by pushing its plug into an electric socket. (Opposite: unplug something)
E.g.1: If you switch a computer on and nothing happens, check that you have plugged it in.
E.g.2: Do you have an adapter? I can’t plug my hairdryer in because it has a British 3 pin plug.
This phrasal verb can be separated. (E.g. 1 & 2)