You Do Need power plug adapter while traveling from Tonga to American Samoa.

Here is Why You Need An Adapter

The outlet and plug type used in American Samoa are A, B, F and I and in Tonga is I. This is how they look like.

Tonga

In Tonga, outlets of type I are in use.

Type I

American Samoa

In American Samoa, outlets of type A, B, F and I are in use.

Type A

Type B

Type F

Type I