You Do Need power plug adapter while traveling from Monaco to British Virgin Islands.

Here is Why You Need An Adapter

The outlet and plug type used in British Virgin Islands are A and B and in Monaco are C, E and F. This is how they look like.

Monaco

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

Type C

Type E

Type F

British Virgin Islands

In British Virgin Islands, outlets of type A and B are in use.

Type A

Type B