You Do Need power plug adapter while traveling from Cambodia 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 Cambodia are A, C and G. This is how they look like.

Cambodia

In Cambodia, outlets of type A, C and G are in use.

Type A

Type C

Type G

Papua New Guinea

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

Type I