..."plug socket"...

I suppose, pedantically speaking, "plug" differentiates it from some other socket, like "electric" guitar differentiates from "acoustic". However, in most contexts, I'm at a loss to know what the other "socket" is (the nearest thing is usually a light bulb, and that's never an option), and in fact, I think most uses of "plug socket" are lazy language, or people who have only ever heard it called that, and don't know why. (Maybe like en_GB speakers say "pavement" for "the pedestrian walkway, generally near a roadway", when obviously half the city is "paved". Granted, "sidewalk" is more obvious in that use, but a "sidewalk" in an internal courtyard, a hundred meters from any vehicular traffic, is also troublesome. I might go with "walkway", except that sometimes connotes some path not fixed to the ground. And "footpath" doesn't need to be paved. (Now I have a headache.))