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

Here is Why You Need An Adapter

The outlet and plug type used in El Salvador are A and B 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

El Salvador

In El Salvador, outlets of type A and B are in use.

Type A

Type B