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

Here is Why You Need An Adapter

The outlet and plug type used in South Korea is F and in Niger are C, D, E and F. This is how they look like.

Niger

In Niger, outlets of type C, D, E and F are in use.

Type C

Type D

Type E

Type F

South Korea

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

Type F