You Do Need power plug adapter while traveling from Vanuatu 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 Vanuatu is I. This is how they look like.

Vanuatu

In Vanuatu, 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