Conversely i bought a thermal label printer sold without a PSU convinced I would have something suitable, i've dozens! Nope!
They're getting junked, it's becoming ridiculous.
I got fooled on that one.
Label printer said it needed "7V".
I connected a 7V supply, and there wasn't enough oomph
to run the motor to advance the label.
Turns out it needs a 7V *unregulated* DC supply, which runs
about 9.8V before you click the print button ("unloaded"), then
drops to 7V while the label comes out (due to the current draw).
That's a transformer based brick and rather large for the
power rating (7V @ 1.2 amps).
I figured I could cheap out and use what I had.
The label gadget had other ideas.