You Do Need power plug adapter while traveling from Austria to Benin.

Here is Why You Need An Adapter

The outlet and plug type used in Benin are C and E and in Austria are C and F. This is how they look like.

Austria

In Austria, outlets of type C and F are in use.

Type C

Type F

Benin

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

Type C

Type E