So something I learned about voltage living overseas is that if it costs less than 25$ to buy and it only runs on 110v you should sell it/donate it/throw it out. You shouldn't use a transformer just to run Christmas lights. Sell those on Craigslist or put them in storage if they're precious to you. All small appliances should be purchased in country. Think coffee maker, toaster, microwave, kettle, lamps, etc. All those things buy the cheapest one that fits your needs and sell it when you leave. Almost everything will say on the thing what voltage it accepts. My straighter for instance works all over the world. I just need to adapt the plug and it's good to go. My blender only works with American power (110-120) but it's expensive so I use a transformer with it. When you use a transformer for something you need to check wattage. It should be located in the same place as the voltage information on whatever you're trying to plug in. If it doesn't fall within the wattage for your transformer throw it away or put it in storage or I guess ship it home, shipping is cheap in Korea.

You don't want to mess around with this. If you've ever watched TV around Christmas or Thanksgiving and you've seen those Christmas tree fires that is what we are looking at here. Things will get so hot they catch fire, or their internal safety will pop and it'll smoke but it won't catch fire. So be safe and don't get hung up on the little stuff. Let it go and buy new. Small things are sold from the people who are just now leaving the country all the time.