Here is an Amazon link, the actual power supply referenced is no longer available, but some alternatives are recommended:
Zynthian will accept input voltage from 9 to 48V. You’d want at least 25 Watts (in order to get 5V at 5 Amps out), something like 9v at 3 Amps or 24V at 1.5Amps, which I think is the ‘official’ Zynthian supply will do the trick.