You Do Need power plug adapter while traveling from Puerto Rico to Dominica.

Here is Why You Need An Adapter

The outlet and plug type used in Dominica are D and G and in Puerto Rico are A and B. This is how they look like.

Puerto Rico

In Puerto Rico, outlets of type A and B are in use.

Type A

Type B

Dominica

In Dominica, outlets of type D and G are in use.

Type D

Type G