Reefton,
on the West coast of the South Island here, was the first town in NZ to have Electricity Generation here, in 1889 I think.
Naturally, the Gas companies here were'nt too impressed with the competition, so they used every method they could to get the plant shut down.
One guy was even killed when he threw a chain over the (then) 190VDC lines, feeding the Streetlighting.
DC 3 wire.
But as wars ensued, Electrical Development was halted.
After WWI, huge leaps were made in reticulating towns with street lights and this carried on and really took off and some houses even had Electric light in them, but WWII intervened, the Black-outs here more or less halted all generation.
But after the war finished, NZ was more or less a playground for new development.
There were all sorts of advertisements around for getting your house reticulated with the new, clean Energy!.
First of all was the Oven/Range, this was so high in Wattage, there is no way you'd put the thing on a plug!.
{I just can't help but relate this, but I came upon an Ad in an old paper I found up in a roof once: The New Appliance For The Modern Woman!, The New Shacklock Electric Range, if your man hasn't bought you one, why not then?, get one yourself, very easy terms!.
Next, was the Refrigerator, it was also permanently wired in.
Anything that did have to be plugged in at the time, was given a 15A round 3-pin plug,
Also bear in mind that there were'nt as many sockets in a house as now.
And most of them were in the kitchen.
In the 60's here, Electrical work went crazy, things like sockets in Bedrooms and other silly things like Shaver sockets in Bathrooms.
To answer your question C-H, the first socket-outlet, hit town over here in 1947, as basic as it was, it did the job!. [Linked Image]

{Sorry, if I rambled on about nothing to get to this}