You Do Need power plug adapter while traveling from Fiji to Mauritius.

Here is Why You Need An Adapter

The outlet and plug type used in Mauritius are C and G and in Fiji is I. This is how they look like.

Fiji

In Fiji, outlets of type I are in use.

Type I

Mauritius

In Mauritius, outlets of type C and G are in use.

Type C

Type G