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

Here is Why You Need An Adapter

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

Nigeria

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

Type D

Type G

Guinea

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

Type C

Type F

Type K