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

Here is Why You Need An Adapter

The outlet and plug type used in Northern Ireland is G and in Vatican City are C, F and L. This is how they look like.

Vatican City

In Vatican City, outlets of type C, F and L are in use.

Type C

Type F

Type L

Northern Ireland

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

Type G