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

Here is Why You Need An Adapter

The outlet and plug type used in Brazil are C and N and in Cayman Islands are A and B. This is how they look like.

Cayman Islands

In Cayman Islands, outlets of type A and B are in use.

Type A

Type B

Brazil

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

Type C

Type N