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

Here is Why You Need An Adapter

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

Guam

In Guam, outlets of type A and B are in use.

Type A

Type B

Guinea

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

Type C

Type F

Type K