You Do Need power plug adapter while traveling from Malta 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 Malta is G. This is how they look like.

Malta

In Malta, outlets of type G are in use.

Type G

Cocos (Keeling) Islands

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

Type I