Bangle.js charger hot and plug melted, how to get a spare.

That's a bit scary - I hadn't had a single report, and I have had two just today.

The magnetic charge cable basically connects USB 5v and GND right through. So, if you let it magnetically attach itself onto something metallic and magnetic (keys, etc) it'll short out (it's a common issue with these types of magnetic cables sadly).

It's always a good idea to disconnect from USB when you're done charging. There was a mention of this in the docs, but given the seriousness of it I have made it more prominent and added mention of it a few extra places - banglejs.com/start for one, where it wasn't before.

Interestingly I've never actually hit the issue because every charger I used seemed to have some overcurrent protection. It seems some devices just provide a whole bunch of USB power with no protection though, and in those cases you can get the melting if it shorts :(

I'm sorry you fell foul of this. I bought a bunch of extra cables - I haven't listed them on the shop yet but I will ensure that I do that soon.

a prctice that the enclosed booklet explains not to do

There's no booklet in the Bangle.js, just a getting started card - and there is no mention of it on there sadly.