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

Here is Why You Need An Adapter

The outlet and plug type used in Mongolia are C and E 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

Mongolia

In Mongolia, outlets of type C and E are in use.

Type C

Type E