Electricity on board all ships is 220v, with 2-pin power outlets. You will need an adapter, and/or converter depending on which electrical appliances you bring with you.
Adapter: Will drop 220v to 110 and can be used with curling irons and hair dryers
Converter: Will only convert from a foreign plug type to a U.S. Plug. If it is a 220v outlet, it will still put 220v out.
Most low power electrical devices (such as cell phones, hearing aids, c-pap machines) will run off of 110v or 220v and can be used with an adapter or a converter. Check your individual devices for power information.