You Do Need power plug adapter while traveling from São Tomé and Príncipe to Norfolk Island.

Here is Why You Need An Adapter

The outlet and plug type used in Norfolk Island is I and in São Tomé and Príncipe are C and F. This is how they look like.

São Tomé and Príncipe

In São Tomé and Príncipe, outlets of type C and F are in use.

Type C

Type F

Norfolk Island

In Norfolk Island, outlets of type I are in use.

Type I