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

Here is Why You Need An Adapter

The outlet and plug type used in Puerto Rico are A and B and in Cocos (Keeling) Islands is I. This is how they look like.

Cocos (Keeling) Islands

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

Type I

Puerto Rico

In Puerto Rico, outlets of type A and B are in use.

Type A

Type B