You Do Need power plug adapter while traveling from Haiti to Dominican Republic.

Here is Why You Need An Adapter

The outlet and plug type used in Dominican Republic are A, B and C and in Haiti are A and B. This is how they look like.

Haiti

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

Type A

Type B

Dominican Republic

In Dominican Republic, outlets of type A, B and C are in use.

Type A

Type B

Type C