You Do Need power plug adapter while traveling from Cocos (Keeling) Islands to Northern Ireland.

Here is Why You Need An Adapter

The outlet and plug type used in Northern Ireland is G and in Cocos (Keeling) Islands is I. This is how they look like.

Cocos (Keeling) Islands

In Cocos (Keeling) Islands, outlets of type I are in use.

Type I

Northern Ireland

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

Type G