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

Here is Why You Need An Adapter

The outlet and plug type used in Cuba are A, B, C and L 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

Cuba

In Cuba, outlets of type A, B, C and L are in use.

Type A

Type B

Type C

Type L