Aussie240,

It looks like that socket says "12.5A 250V". Am I correct?

I've never seen that rating on US-made devices, although some early US parallel and T-slot devices are rated 250V or even 300V.

Although the polarized "NEMA 1-15" became the standard receptacle in the US by the '30s, polarized plugs were just about rare as hen's teeth until 1978. That's not to say they didn't exist at all. The bathroom fans in my 1971 house had polarized plugs, before I replaced them with new ones.