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

Here is Why You Need An Adapter

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

Saint Lucia

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

Type G

Equatorial Guinea

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

Type C

Type E