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

Here is Why You Need An Adapter

The outlet and plug type used in Thailand are A, B, C and O 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

Thailand

In Thailand, outlets of type A, B, C and O are in use.

Type A

Type B

Type C

Type O