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

Here is Why You Need An Adapter

The outlet and plug type used in Dominica are D and G and in Northern Ireland is G. This is how they look like.

Northern Ireland

In Northern Ireland, outlets of type G are in use.

Type G

Dominica

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

Type D

Type G