You Do Need power plug adapter while traveling from Italy to Niue.

Here is Why You Need An Adapter

The outlet and plug type used in Niue is I and in Italy are C, F and L. This is how they look like.

Italy

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

Type C

Type F

Type L

Niue

In Niue, outlets of type I are in use.

Type I