OSPi has a switching regulator that generates 5V DC from 24V AC input power. By “single power supply” it means the same 24V AC power is used to drive solenoid valves as well as powering RPi.
For users outside of US/Canada/Mexico, please find 24V AC power supplies locally in your country. AC power adapters are NOT regulated and the ones we sell are only rated for 110V input. So it cannot be used in other countries.