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

Here is Why You Need An Adapter

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

Vanuatu

In Vanuatu, outlets of type I are in use.

Type I

Grenada

In Grenada, outlets of type G are in use.

Type G