You Do Need power plug adapter while traveling from Yemen to Montserrat.

Here is Why You Need An Adapter

The outlet and plug type used in Montserrat are A and B and in Yemen are A, D and G. This is how they look like.

Yemen

In Yemen, outlets of type A, D and G are in use.

Type A

Type D

Type G

Montserrat

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

Type A

Type B