You Do Need power plug adapter while traveling from Solomon Islands 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 Solomon Islands are G and I. This is how they look like.

Solomon Islands

In Solomon Islands, outlets of type G and I are in use.

Type G

Type I

Vatican City

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

Type C

Type F

Type L