The standard electrical voltage in all the countries we travel to is 220/240 volts AC, 50Hz except in Japan, which is 110 volts. Since the hotels we stay at cater to international travellers, you do not need to bring your own adapter plugs or waste time trying to figure out if the power sockets would work with your battery charger.
Nowadays, most personal electronic devices such as digital cameras and smart phones are designed to work with voltages between 110 and 240. Check your devices before going on the trip.
In rare circumstances (Nintendo game consoles, for example) where you’ll need a transformer to recharge the battery, you can borrow one from the hotel. In other words, don’t bother to go buy a transformer just for this trip.