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

Here is Why You Need An Adapter

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

Solomon Islands

In Solomon Islands, outlets of type G and I are in use.

Type G

Type I

Pitcairn Islands

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

Type I