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

Here is Why You Need An Adapter

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

Rwanda

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

Type C

Type E

Type F

Type G

Sri Lanka

In Sri Lanka, outlets of type G are in use.

Type G