You Do Need power plug adapter while traveling from Argentina 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 Argentina are C and I. This is how they look like.

Argentina

In Argentina, outlets of type C and I are in use.

Type C

Type I

Cocos (Keeling) Islands

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

Type I