You Do Need power plug adapter while traveling from Monaco 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 Monaco are C, E and F. This is how they look like.

Monaco

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

Type C

Type E

Type F

Vatican City

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

Type C

Type F

Type L