Does it risk damaging the appliance you're trying one out on though , even if it appears to fit?
That's a good point, well worth checking. There are three things to check:
POLARITY: Some devices have a positive tip, some negative. There's no simple rule as to which is which. More details here: https://en.wikipedia.org/wiki/Polarity_symbols
VOLTAGE: If the power supply gives out more voltage than your device uses (i.e. PSU output is 12V and your device is 7.5v) then you risk damage or fire.
CURRENT (amps): This is a little more forgiving. You must make sure your power supply can deliver the current your device requires. If the power supply gives out more (eg 1.2amps and your device is 750 miliamps) then that's fine, your device will just take what's needed.
But it doesn't work the other way. If your device is 1amp and your charger is 1/2 an amp, it won't charge or power correctly. A lot of car cigarette lighter USB chargers are like this and won't deliver the right ampage.