Tried charging my phone and my camera this morning. When I plugged them in, I got an error message on the screen saying "not charging". Huh? Clearly, the devices were getting some power, but only enough to realise that they weren't getting enough, and to tell me as much.
I took my phone, and related accessories, to a mobile phone dealer in Xalapa. With some seriously crap Spanish, I managed to convey to them that I needed some sort of transformer in order to make it charge.
Most fortunately, there was an electrico across the road, and the phone lady kindly escorted me over there, and helped explain my problem to the staff there.
I now have a 110V to 240V converter / transformer, which the electrico gave me for about 50 pesos; and now I can charge my devices just fine.