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

Here is Why You Need An Adapter

The outlet and plug type used in Chad are C, D, E and F and in Cook Islands is I. This is how they look like.

Cook Islands

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

Type I

Chad

In Chad, outlets of type C, D, E and F are in use.

Type C

Type D

Type E

Type F