Don't bring a voltage converter. You won't need it. Every laptop and phone charger can run 110-240V. Also, don't bring any device that requires a voltage converter (e.g., kitchen appliances, a blow dryer etc.). Just buy new stuff here.

FYI: A voltage converter is a big, heavy device that plugs into the wall. An adapter is small and just changes the plug. You can buy adapters in Korea for 2,000 won or less.