Hutch,
No I don't think that configuration of plug was used in Europe as far as I am aware it was either 2 round pins or light bulb sockets. Although I am not 100% sure as Europe's had endless different standards in the old days. I know 127V remained in exsistance in parts France post WWII but I have never seen a NEMA style outlet even in the oldest French house.
Centre tapped systems with 2 hot terminals supplying 220V between them have remained in service for much longer though. This is partly the reason that connector systems like Schuko etc are not polarised
I guess NEMA sockets would prevent the accidental connection of 127V appliences to 220V sockets though so would make a lot of sense in installations where the system is still in use.
As for the British DC system I think paul UK could give more detail but as far as I know they used BS546 style 3-pin polorised plugs and a 2-pin ungrounded and unpolarised plug which was similar to Europlugs but with shorter fatter pins. (not unlike the current UK shaver plug)
The old British system had a LOT of plug configurations all of which were incompatable so most homes were full of adaptors.
I am also not 100% sure when they standardised on 240V 50Hz or what other systems were around.
The Republic of Ireland was very boring and never really used DC systems in domestic/industrial supply in the 20th century. Although various local arrangements exsisted in the late 1800s and into the 1910s and even early 20s. The ESB rapidly standardised on 220V 50hz (with a earth-bonded neutral) and 380V 4-wire 3-phase in 1926 and the independent supply systems were bought up by the ESB under an act of parliament, connected to the fledgling national grid and standardised.
So I have never seen reminants of DC systems other than in UK photos.
