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

Here is Why You Need An Adapter

The outlet and plug type used in Sierra Leone are 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

Sierra Leone

In Sierra Leone, outlets of type D and G are in use.

Type D

Type G