You Do Need power plug adapter while traveling from Equatorial Guinea to Sri Lanka.

Here is Why You Need An Adapter

The outlet and plug type used in Sri Lanka 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

Sri Lanka

In Sri Lanka, outlets of type G are in use.

Type G