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

Here is Why You Need An Adapter

The outlet and plug type used in Saint Lucia is G and in Equatorial Guinea are C and E. This is how they look like.

Equatorial Guinea

In Equatorial Guinea, outlets of type C and E are in use.

Type C

Type E

Saint Lucia

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

Type G