South Korea's standard electricity supply is 220 volts at 60 Hz. The common wall outlets are Type C and Type F, with two round holes.
If your plug has a different shape, you need a plug adapter. An adapter only changes the physical connection; it does not change the voltage. Before plugging in any device, read the input label on its charger or power supply. If the label includes 220 V (many modern chargers show a range such as 100–240 V), you normally only need the correct plug adapter. If your device is rated only for a lower voltage, do not use it directly on a Korean outlet; use an appropriate voltage converter or leave the device at home.
Pay extra attention to high-power appliances such as hair dryers, curling irons, heating devices and some older chargers because they are more likely to be single-voltage. If you are unsure, ask the manufacturer or your accommodation rather than testing the device in the socket.
Do not assume a hotel USB port or borrowed charger is suitable for every device. Use a reputable charger that matches your device and check its printed input range.
Practical next step: before departure, photograph the input label of each important charger, pack a Type C/F-compatible adapter if needed, and identify any device that requires actual voltage conversion.