You Do Need power plug adapter while traveling from Cocos (Keeling) Islands to United States of America (US) USA.

Here is Why You Need An Adapter

The outlet and plug type used in United States of America (US) USA 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

United States of America (US) USA

In United States of America (US) USA, outlets of type A and B are in use.

Type A

Type B