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

Here is Why You Need An Adapter

The outlet and plug type used in Cook Islands is I and in Eritrea are C and L. This is how they look like.

Eritrea

In Eritrea, outlets of type C and L are in use.

Type C

Type L

Cook Islands

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

Type I