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

Here is Why You Need An Adapter

The outlet and plug type used in Niger 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

Niger

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

Type C

Type D

Type E

Type F