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

Here is Why You Need An Adapter

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

Tonga

In Tonga, outlets of type I are in use.

Type I

Rwanda

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

Type C

Type E

Type F

Type G