From what I recall, the vast majority of bathrooms in almost every hotel we stay at throughout the world, usually have a 110VAC outlet. The proviso usually says it's just for electric shavers, but I've used it for both my computer as well as my cell phone, and never had a problem. The other technique is to borrow one from the hotel desk, as they usually have them. Or you could just shell out a few bucks and not bother with any of the above.