You Do Need power plug adapter while traveling from Gabon to Vanuatu.

Here is Why You Need An Adapter

The outlet and plug type used in Vanuatu is I and in Gabon is C. This is how they look like.

Gabon

In Gabon, outlets of type C are in use.

Type C

Vanuatu

In Vanuatu, outlets of type I are in use.

Type I