By Rick Steves
Europe's electrical system is different from ours in two ways: the voltage of the current and the shape of the plug.
American appliances run on 110 volts, while European appliances are 220 volts. Most gadgets are "dual voltage," which means they work on both American and European current. If you see a range of voltages printed on the item or its plug (such as "110–220"), you're OK in Europe. Some older appliances have a voltage switch marked 110 (US) and 220 (Europe) — switch it to 220 as you pack.
Even older devices (and some handheld gaming systems) aren't equipped to deal with the voltage difference — you'll need a separate, bulky converter. (Consider replacing your appliance instead.)
A small adapter allows American-style plugs (two flat prongs) to fit into British or Irish outlets (which take three rectangular prongs) or Continental European outlets (which take two round prongs). Adapters are inexpensive — bring a handful. Even on a Continent-only trip, I keep a British adapter on hand for London layovers. Secure your adapter to your device's plug with electrical or duct tape; otherwise it can easily get left behind in the outlet (hotels and B&Bs sometimes have a box of abandoned adapters — ask). Many sockets in Europe are recessed into the wall; your adapter should be small enough so that the prongs seat properly in the socket. (Although you can get universal adapters that work Europe-wide — or even worldwide, these tend to be large, heavy, and more expensive.)
Although sockets in Switzerland and Italy differ from others on the Continent, most Continental adapters work just fine. (Swiss and Italian outlets accept plugs with three slim round prongs arranged in a triangular shape; two-pronged adapters work as long as they don't have the thicker "Schuko" style prongs — and if the body of the adapter is small enough to fit in the recessed outlet.) If, for some reason, your adapter doesn't work in your hotel, just ask for assistance; hotels with unusual sockets will invariably have the right adapter to loan you.
Some budget hotel rooms have only one electrical outlet, occupied by the lamp. Hardware stores in Europe sell cheap three-way plug adapters that let you keep the lamp on while you charge your camera battery and smartphone.