You Do Need power plug adapter while traveling from Gambia to Monaco.

Here is Why You Need An Adapter

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

Gambia

In Gambia, outlets of type G are in use.

Type G

Monaco

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

Type C

Type E

Type F