24V 40VA Control Transformer, Primary 120/208/240V, Secondary 24V Isolation Transformer with Foot Mount for HVAC Furnace Multi Tap

The Shelly Uni is only for sensors; it has no relays on it. You're looking for some kind of device clearly marked with "Common", "NC"/"Normally Closed", and "NO"/"Normally Open" Connections. Once again, that's a DC, Direct Current, power supply. You need an AC (Alternating current) Power supply to drive the actuators. I linked one above; this 24 volt AC transformer is your power supply.

You buy a 24v AC Valve actuator (Getting a Pentair one will guarantee fit, but there are cheaper off-brand models available; they wire up the same), a 24 volt transformer, Some 1 amp fuses and holders, and some manner of relay with NO and NC Contacts (For example, This Zooz Universal Relay -- note, this is not the same as the multirelay, but can control up to 2 valve actuators). Wire it up according to this diagram, with Transformer 24V Red to Universal Relay (UR) Common, Actuator Red to UR-NC, Actuator White to UR-NO, and Actuator Black to Transformer 24V Green. Added bonus of the Zooz: You can use the 24V AC off the transformer to power the Universal Relay as well, eliminating the USB Power supply in the watertight box you're putting everything in (you are putting everything in a watertight box, right?) This only gets you straight on/off; no position control of the valve, but it's cheaper than most of the Pentair first party solutions, and IMO more reliable. Note, I'm a proponent of Z-Wave for pool valves just because Z-Wave LR usually has no problems reaching out to pool houses, but use whatever you've got in your install already.