You Do Need power plug adapter while traveling from Nepal to Saint Lucia.

Here is Why You Need An Adapter

The outlet and plug type used in Saint Lucia is G and in Nepal are C, D and M. This is how they look like.

Nepal

In Nepal, outlets of type C, D and M are in use.

Type C

Type D

Type M

Saint Lucia

In Saint Lucia, outlets of type G are in use.

Type G