You Do Need power plug adapter while traveling from Bulgaria 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 Bulgaria are C and F. This is how they look like.

Bulgaria

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

Type C

Type F

Equatorial Guinea

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

Type C

Type E