You Do Need power plug adapter while traveling from Fiji to Antigua and Barbuda.

Here is Why You Need An Adapter

The outlet and plug type used in Antigua and Barbuda are A and B and in Fiji is I. This is how they look like.

Fiji

In Fiji, outlets of type I are in use.

Type I

Antigua and Barbuda

In Antigua and Barbuda, outlets of type A and B are in use.

Type A

Type B