The Spruce Controller requires a 24 VAC input with 400 mA minimum current. Each Spruce Controller includes a 120 V transformer with a 2.1 mm x 5.5 mm barrel plug. Note that this is very different from a 24V DC power supply, which can be small and compact (an AC transformer typically has a large ‘brick’ in the power supply).
If desired, power can be delivered to the unit via bare wires.