You Do Need power plug adapter while traveling from Brunei to Guinea.

Here is Why You Need An Adapter

The outlet and plug type used in Guinea are C, F and K and in Brunei is G. This is how they look like.

Brunei

In Brunei, outlets of type G are in use.

Type G

Guinea

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

Type C

Type F

Type K