The world runs on two types of electricity: 110/125V or 220/240V. North American devices run on 110/125V electricity while the majority of the world runs on 220/240V. Converters and transformers change the voltage of electricity to match the voltage of your device.
If your appliance is not dual-voltage, you’ll need a converter to step-down the 220-240 volt current in the country you are visiting to the 110-120 volt US current. If you fail to use a converter, and plug directly into a 220v/250v outlet, your appliance will spark like the 4th of July and may even black-out your hotel. As a result, you’ll most likely be introduced to the universal definition of "not good". If you're traveling with certain devices, such as hair dryers and kettle, you may also need a travel voltage converter.
Your device should say the range of voltage it can handle. This should be on a sticker or on the plug or device itself. Some devices are internationally compliant and can handle the voltage (my iPhone charger is fine to use without a converter). Others WILL NOT and you will need to purchase a converter or use a different device. (Kinda’s Chi straightener actually started smoking in Wales and was destroyed. She now travels with a tiny straightener that is made to handle both voltages).
We've selected some of the best voltage converters below. But if you're not sure what type of voltage converter or adapter you need - this handy Voltage Converter Guide explains all about international plug adapers and travel voltage converters.
If your gadget doesn't support the 2 voltages, you'll have to get an adapter that changes the 220 coming from the wall to 110 for the appliance. These can be expensive. If we're talking about a hairdryer, you're probably better off getting a new hairdryer overseas.