Sockets & plugs
Rwanda uses 230V, 50Hz with sockets and plugs Type C and Type J.
Type C
Type J
Adapters and transformers
Sockets & plugs
You may need an adapter while in Rwanda.
Frequency
Frequency difference is generally not a problem - almost all items (except some types of clocks) will work on both and you shouldn't worry about it.
Voltage
If there is a voltage difference between countries, you probably won't need a transformer/converter if you use recent devices and appliances because they all work worldwide automatically.