I know that 2 pin sockets, not unlike modern "europlugs" were in use in Ireland as early as the 1920s.
They were initially for connecting portable lamps, irons, kettles and other heating appliences.
Scraping side-earthed plugs have been around for quite sometime too. (as were old-style 3-pin british plugs)
More complicated appliences like vacuum cleaners, washing machines etc didn't really become generally available until the 1950s. WWII held up development signifigantly.
Fridges made a slightly pre WWII appearance too. Often using schuko-like plugs in IRL. (Remember the UK and IRL arn't that hot, so they were not perhaps as essential as in NYC and most food was bought and consumed on the same day. Shops had fridges quite early on.)
The only high-tech appliences you'd find pre WWII were valve-radios. Often connected via a 2-pin plug or into a bayonet light socket.
When was schuko introduced?
It seems to be around quite a while.
