It was even worse at the start of the 20th century. There were no national standards, and different companies came up with their own plug/socket systems to save early adopters from having to wire everything in directly. If your house came with electrical sockets, their type often depended on what the builder could get cheaply. National standards arise when governments and standards bodies picked winners. (The US ended up choosing one American manufacturer’s flat-pinned system, though another one, with the pins rotated at a 45° angle, ended up being adopted in Australia, New Zealand and Argentina.)

Occasionally you see odd-looking sockets on old buildings, often with a distinctly early 20th century styling. Some places keep them for distinct uses (in railway stations in Britain you sometimes see sockets that look like the normal British ones only with the pins rotated, presumably reserved for cleaning equipment).

There have been moves to establish a unified international standard (which looks like a more compact version of the Swiss plug), though only Brazil has adopted it (and South Africa is transitioning gradually to it from the old British system it inherited).