You Do Need power plug adapter while traveling from El Salvador to Papua New Guinea.

Here is Why You Need An Adapter

The outlet and plug type used in Papua New Guinea is I and in El Salvador are A and B. This is how they look like.

El Salvador

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

Type A

Type B

Papua New Guinea

In Papua New Guinea, outlets of type I are in use.

Type I