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

Here is Why You Need An Adapter

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

Belgium

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

Type C

Type E

Vatican City

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

Type C

Type F

Type L