You Do Need power plug adapter while traveling from Barbados 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 Barbados are A and B. This is how they look like.

Barbados

In Barbados, 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