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

Here is Why You Need An Adapter

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

American Samoa

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

Type A

Type B

Type F

Type I

Sri Lanka

In Sri Lanka, outlets of type G are in use.

Type G