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

Here is Why You Need An Adapter

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

Vanuatu

In Vanuatu, outlets of type I are in use.

Type I

Slovakia

In Slovakia, outlets of type C and E are in use.

Type C

Type E