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

In Gibraltar, outlets of type G are in use.

Type G

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

Type A

Type B

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