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

Here is Why You Need An Adapter

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

Sri Lanka

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

Type G

Niger

In Niger, outlets of type C, D, E and F are in use.

Type C

Type D

Type E

Type F