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

Here is Why You Need An Adapter

The outlet and plug type used in Monaco are C, E and F 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

Monaco

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

Type C

Type E

Type F