If you are not in US/Canada/Mexico, then you need to find a power adapter yourself. Our adapter only takes 110~120VAC input (if you were to use it, you would have to use a step-down transformer, which will be too complicated).
The Rail mounted PSU you found seems fine — it takes 240VAC input, outputs 24VAC, and rated 1amp, so that’s sufficient for AC-powered OpenSprinkler.