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

Here is Why You Need An Adapter

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

Niger

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

Type C

Type D

Type E

Type F

Brazil

In Brazil, outlets of type C and N are in use.

Type C

Type N