I recently inherited a Kim-1, the first computer I ever used. It came without a power supply. I've got a suitable edge-connector now, but I have very limited knowledge of electronics and don't have any other equipment aside from a soldering iron, multimeter and various wall warts and USB chargers. I don't have a bench PSU.

I know questions about Kim1 PSUs have been asked before, but I have a specific question:

Assuming I don't want to use the cassette interface, is there any reason why I can't just power the Kim-1 from, for example, a good quality (i.e. genuine Apple) USB charger or other 5V PSU rated at 1A or higher? (This is how I power my Ben Eater-style 6502 breadboard computer, although that's worth rather less!)

Grateful for any practical advice!

Welcome! With a high quality USB charger, you should be fine. (Edit: I'm assuming that information from elsewhere tells you that 1A is enough current. Edit: 1.2A is stated in the manual.)

Of course, if it doesn't just work, switch off immediately. It's possible that there will be some component failures - but that's an adventure for another day.

Edit: for some modern computers, the 5V from a charger won't be enough, mostly due to voltage drop on the wires, but I think the KIM-1 won't be so picky. And there's no harm if you find you've under-volted it and it doesn't work well.

There is also a 12V supply, but from a quick look at the schematic it's only needed for the op-amp on the cassette input. It's probably OK to leave it unconnected.

Just a quick thought: ideally you'd want some defence against a short circuit on the board. More recent boards might have tantalum capacitors, for example, which can fail as a short. If you don't have a supply which can apply a current limit, you could possibly damage the supply. (I would hope a high-quality USB supply could survive, but I don't know that.)

And even more important, be absolutely sure you're connecting the supply the right way around, otherwise you could damage the KIM-1. (I doubt it has protection diodes.)

The KIM-1 Users Manual says exactly that:

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Curt J. Sampson - github.com/0cjs

Thank you everyone, very helpful advice! I plan to quadruple-check I have the polarity correct, that seems to be a very real risk if I've understood correctly that GND and +5V are on opposite sides of the same pin!