Cuba uses both the North American system of 110 volts, 60 cycles, and the 220-volt European system. North American–style plugs are the norm here. If your appliances are dual-voltage (as many laptop computers are), you'll need only an adapter. However, if they're strictly 110 volts, as most appliances sold in North America are, plugging them into a 220-volt outlet will destroy them. Outlets are often marked either 110 or 220, but if they aren't, be sure to ask what the voltage is before plugging in an appliance. Consider buying a universal adapter; Swiss Army's adapters have several types of plugs in one handy unit.
Although conditions are improving, blackouts are still an occasional reality. Most hotels have a backup power system, but these are designed to keep electricity flowing only to lights in lounges and hallways and to emergency lamps in guest rooms.