A automotive battery charger works fine
Lots of newer battery chargers need a load on them to supply a decent number of amps. You can hookup an old battery and use it, but an old PC ATX power supply is ideal. They'll put out between 10-40 amps at 6 or 12v and most have a small fan to keep them cool.
You can also often get one free (or nearly free) so there's no worry if you toast it.
To setup for electrolysis, cutoff the connectors.
- Strip and connect all the black wires together (ground)
- Strip and connect the green wire to the bundle of black wires (this is connected to the switch on a PC. You need to ground this for the PS to stay on.)
- Strip and connect all the yellow wires together (+12v)
- Strip and connect all the red wires together (+5v)
Connect some clips to your wire bundles and you're ready to go.
If you power supply doesn't have an on/off switch you can route the green wire through a switch and use that.