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

Here is Why You Need An Adapter

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

Dominica

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

Type D

Type G

Niger

In Niger, outlets of type C, D, E and F are in use.

Type C

Type D

Type E

Type F