One of the options seems to be a step down transformer paired with Rachio's original 110v supply.
Amazon has one here (link) that is advertised for 100W continuous use . Since Rachio needs only 30W, it should be a good fit.
Seems like many of the AC transformers are marked with voltage under load, as in: if you run X transformer under full load, voltage will be Y. As such, one thing to look out for is to make sure that transformer is not too overrated above 1Amp or 24VA as not to have a high, no-load voltage.