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

Here is Why You Need An Adapter

The outlet and plug type used in Sri Lanka is G and in Botswana are D and G. This is how they look like.

Botswana

In Botswana, outlets of type D and G are in use.

Type D

Type G

Sri Lanka

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

Type G