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

Iceland

In Iceland, outlets of type C and F are in use.

Type C

Type F

Cocos (Keeling) Islands

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

Type I