Any reason why you are using a DC power supply? Since the controller uses triac to control valves, if you use a DC power supply, you will only be able to turn on a sprinkler valve and once on it cannot be turned off (because DC does not have zero crossings).
In any case, if you are using a DC power supply, you have to observe the polarity: on the 24VAC terminal, the pin closer to the USB port is tied to ground, so you should connect that to the negative wire of your DC power supply.