You Do Need power plug adapter while traveling from Pitcairn Islands to Wales.

Here is Why You Need An Adapter

The outlet and plug type used in Wales is G and in Pitcairn Islands is I. This is how they look like.

Pitcairn Islands

In Pitcairn Islands, outlets of type I are in use.

Type I

Wales

In Wales, outlets of type G are in use.

Type G