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

Here is Why You Need An Adapter

The outlet and plug type used in Northern Ireland is G and in South Africa are C, M and N. This is how they look like.

South Africa

In South Africa, outlets of type C, M and N are in use.

Type C

Type M

Type N

Northern Ireland

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

Type G