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

Here is Why You Need An Adapter

The outlet and plug type used in Thailand are A, B, C and O 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

Thailand

In Thailand, outlets of type A, B, C and O are in use.

Type A

Type B

Type C

Type O