Each channel can drive up to 1 amp. Are you sure your valve draws 0.6A at holding state? Most sprinkler valves draw about 0.2 to 0.25A at holding state (and 0.6A impulse, which is only for a split second when it opens). In any case, the power adapter should be ok to drive a single 0.6A valve as long as you have only one open at a time. You can always buy a 24VAC adapter with larger current rating if needed.