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

Here is Why You Need An Adapter

The outlet and plug type used in South Korea is F and in Pitcairn Islands is I. This is how they look like.

Pitcairn Islands

In Pitcairn Islands, outlets of type I are in use.

Type I

South Korea

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

Type F