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

Here is Why You Need An Adapter

The outlet and plug type used in Slovakia are C and E and in Vatican City are C, F and L. This is how they look like.

Vatican City

In Vatican City, outlets of type C, F and L are in use.

Type C

Type F

Type L

Slovakia

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

Type C

Type E