I think I have an alternate solution – TP-LINK TL-POE10R POE Splitter. This box takes in the Ethernet connection that carries the POE and splits out the power to a separate socket.
However, now need to confirm that the power supplied is compatible with the OpenSprinkler. Seems that the splitter only provides 12V and the OpenSprinkler controller and sprinkler valves require 24V. I have seen sprinkler valves running at 9V or 12V however? Does this make a difference?