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

Here is Why You Need An Adapter

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

Tajikistan

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

Type C

Type F

Tonga

In Tonga, outlets of type I are in use.

Type I