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

Here is Why You Need An Adapter

The outlet and plug type used in Monaco are C, E and F and in Isle of Man are C and G. This is how they look like.

Isle of Man

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

Type C

Type G

Monaco

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

Type C

Type E

Type F