You Do Need power plug adapter while traveling from Brazil to Cocos (Keeling) Islands.

Here is Why You Need An Adapter

The outlet and plug type used in Cocos (Keeling) Islands is I and in Brazil are C and N. This is how they look like.

Brazil

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

Type C

Type N

Cocos (Keeling) Islands

In Cocos (Keeling) Islands, outlets of type I are in use.

Type I