You Do Need power plug adapter while traveling from South Korea to Thailand.

Here is Why You Need An Adapter

The outlet and plug type used in Thailand are A, B, C and O and in South Korea is F. This is how they look like.

South Korea

In South Korea, outlets of type F are in use.

Type F

Thailand

In Thailand, outlets of type A, B, C and O are in use.

Type A

Type B

Type C

Type O