Background information
History

An American socket alongside a British power outlet
Like most countries in the Caribbean and North America, Montserrat uses American-style plugs (types A and B), which are standard throughout the region for convenience and compatibility.
Because of its status as a British Overseas Territory, British type G receptacles can also be found. While American sockets are standard in all households and hotels across the island, only about a quarter of them also provide British power outlets. So, if you want to be on the safe side as a tourist, it is best to pack an adapter that fits type A or B wall outlets.
Keep in mind, however, that travel adapters simply allow a device from one country to be plugged into the wall outlet of another country, but they do not convert electricity. Despite using American-style plugs, Montserrat's electricity does not run at 120 volts, but at 230 volts, identical to the voltage in the UK. This is why tourists from North and Central America - where the voltage is 120 volts - have to be sure that their appliances can deal with the electricity coming out of the socket. Always check your device's voltage listing: "INPUT: 100-240 V" means that your device is multi-voltage and that it will work with any voltage between 100 V and 240 V. Luckily, many travel gadgets (such as laptops or phone chargers) are multi or dual voltage, so most tourists will not have a problem. If your device is single voltage (e.g. "INPUT: 120V"), you will need a transformer to step down the voltage.
Click here for a global map showing the spread of the different plug types used around the world.
Click here for a detailed list of the countries of the world with their respective plug and outlet types, voltage and frequency.