You Do Need power plug adapter while traveling from Monaco to Isle of Man.

Here is Why You Need An Adapter

The outlet and plug type used in Isle of Man are C and G 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

Isle of Man

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

Type C

Type G