@Stefan: yes plus much more.
@Etienne: maybe yes, the SIO port does provide a 5V out (unlikely serial ports of computing products like f.i. Commodore) and a few devices actually ran from that power, one was a cassette recorder (XC12) so it seems to be capable of providing at least some power, at least enough to power the motor of the tape drive, which is relatively power hungry. So....following that it might well be possible indeed but I'm not sure if the device actually does put out the 5V.