Currently standard household electricity in Korea is 220V, 60Hz. Our electricity supply is very stable and seldom goes out.
It used to be all 100V, 60Hz upto about 1973.
Because 220V was more efficient, Korean government made a 32 year plan started in 1973 to completely change from 100V to 220V by 2005.
And since 1973 all newly built buildings were required to install 110V and 220V as well.
Nowadays all buildings are built with 220V only and all old buildings were completely converted to 220V.
During the coversion time period, most homes used transformers to convert 220V to 110V to use their 110V appliances.
Foreign hams who come to Korea can purchase the transformers at local hardware stores to use their 100V - 120V equipments.
A 1KW, 220V to 110V transformer (we call it down transformer) costs about $20-$30US in Korea.
Radio equipments designed for 220-240V, 50Hz work well at 220V, 60Hz according to my experience.
Manufacturers of electrical equipments design them to work at +-10% of specified voltage range.
So it is no problem to use 100V-120V equipments at 110V and 200V-240V equipments at 220V.
However, equipments with motors like refrigerators or vacuum cleaners or fans will run 20% faster at 60Hz than at 50Hz.
And transformers designed for 50Hz work well at 60Hz according to my experience.
The 220V, 60Hz plug and receptacle are the same size as they use in China, Mongolia, Vietnam, France, Spain, Indonesia and most Europe, I believe. These are the countries HL1FB visited and verified.
The 100V, 60Hz plugs and receptacles we used to use are the same ones currently used in US, Canada, Philippines and Japan.