Similarly, I've noticed en_GB speakers (and occasionally writers) using the phrase "plug socket" more and more. Given that pretty much every (physical) socket takes a plug of some sort this comes across as more redundant than oxymoronic. Usually they mean to refer to a power socket (typically a standard 3-pin 13-amp ring-main power socket). Why they don't call it that only they can say.
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.))
Quantum Mechanics: The dreams stuff is made of