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

Here is Why You Need An Adapter

The outlet and plug type used in Dominica are D and G and in Guadeloupe are C and E. This is how they look like.

Guadeloupe

In Guadeloupe, outlets of type C and E are in use.

Type C

Type E

Dominica

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

Type D

Type G