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

Here is Why You Need An Adapter

The outlet and plug type used in Cayman Islands are A and B 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

Cayman Islands

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

Type A

Type B