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

Here is Why You Need An Adapter

The outlet and plug type used in Sri Lanka is G 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

Sri Lanka

In Sri Lanka, outlets of type G are in use.

Type G