You Do Need power plug adapter while traveling from Vatican City to United States of America (US) USA.

Here is Why You Need An Adapter

The outlet and plug type used in United States of America (US) USA are A and B 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

United States of America (US) USA

In United States of America (US) USA, outlets of type A and B are in use.

Type A

Type B