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

Here is Why You Need An Adapter

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

Ethiopia

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

Type C

Type F

Type G

Tonga

In Tonga, outlets of type I are in use.

Type I