You Do Need power plug adapter while traveling from Equatorial Guinea to Costa Rica.

Here is Why You Need An Adapter

The outlet and plug type used in Costa Rica are A and B 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

Costa Rica

In Costa Rica, outlets of type A and B are in use.

Type A

Type B