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

Here is Why You Need An Adapter

The outlet and plug type used in Zambia are C, D and G and in Papua New Guinea is I. This is how they look like.

Papua New Guinea

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

Type I

Zambia

In Zambia, outlets of type C, D and G are in use.

Type C

Type D

Type G