You Do Need power plug adapter while traveling from Nauru to Tajikistan.

Here is Why You Need An Adapter

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

Nauru

In Nauru, outlets of type I are in use.

Type I

Tajikistan

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

Type C

Type F