You Do Need power plug adapter while traveling from São Tomé and Príncipe to Cook Islands.

Here is Why You Need An Adapter

The outlet and plug type used in Cook Islands is I and in São Tomé and Príncipe are C and F. This is how they look like.

São Tomé and Príncipe

In São Tomé and Príncipe, outlets of type C and F are in use.

Type C

Type F

Cook Islands

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

Type I