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

Here is Why You Need An Adapter

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

French Guiana

In French Guiana, outlets of type C, D and E are in use.

Type C

Type D

Type E

South Korea

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

Type F