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

Here is Why You Need An Adapter

The outlet and plug type used in Solomon Islands are G and I 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

Solomon Islands

In Solomon Islands, outlets of type G and I are in use.

Type G

Type I