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

Here is Why You Need An Adapter

The outlet and plug type used in Pitcairn Islands is I 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

Pitcairn Islands

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

Type I