You Do Need power plug adapter while traveling from Tokelau to Serbia.

Here is Why You Need An Adapter

The outlet and plug type used in Serbia are C and F and in Tokelau is I. This is how they look like.

Tokelau

In Tokelau, outlets of type I are in use.

Type I

Serbia

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

Type C

Type F