You Do Need power plug adapter while traveling from Wales to Sint Maarten.

Here is Why You Need An Adapter

The outlet and plug type used in Sint Maarten are A and B and in Wales is G. This is how they look like.

Wales

In Wales, outlets of type G are in use.

Type G

Sint Maarten

In Sint Maarten, outlets of type A and B are in use.

Type A

Type B