You Do Need power plug adapter while traveling from Liberia to Cook Islands.

Here is Why You Need An Adapter

The outlet and plug type used in Cook Islands is I and in Liberia are A, B, C and F. This is how they look like.

Liberia

In Liberia, outlets of type A, B, C and F are in use.

Type A

Type B

Type C

Type F

Cook Islands

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

Type I