Converters & transformers
As their names suggest, converters and transformers change the voltage of the power that runs through them. With the right converter or transformer, you can run a 100/120V single-voltage appliance in a 220/240V country, and vice versa.
Converters and transformers are appropriate for different kinds of devices. A converter provides high-wattage power (usually up to 2,000 watts) for electric items like hair dryers, room fans, and shaving razors, whereas a transformer provides low-wattage power (usually up to 50 watts) for electronics like cameras and digital clocks. Luckily, many products are two-in-ones that can be switched between high-wattage converting and low-wattage transforming as necessary. Be careful not to power electronics on high-wattage converters—since most electronics are dual- or multi-voltage, you’re better off simply getting an adapter for those.
Pros: Converts power to the right voltage, allowing the use of any appliance in any country.
Cons: Larger, heavier, and more expensive than an adapter. Unnecessary if all your devices are dual- or multi-voltage.