You Do Need power plug adapter while traveling from Pitcairn Islands 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 Pitcairn Islands is I. This is how they look like.

Pitcairn Islands

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

Type I

Thailand

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

Type A

Type B

Type C

Type O