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

Here is Why You Need An Adapter

The outlet and plug type used in Guinea are C, F and K 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

Guinea

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

Type C

Type F

Type K