You Do Need power plug adapter while traveling from Iceland to Mayotte.

Here is Why You Need An Adapter

The outlet and plug type used in Mayotte are C and E 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

Mayotte

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

Type C

Type E