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

Here is Why You Need An Adapter

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

Bhutan

In Bhutan, outlets of type C, D and G are in use.

Type C

Type D

Type G

Guinea

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

Type C

Type F

Type K