You Do Need power plug adapter while traveling from China to Guinea-Bissau.

Here is Why You Need An Adapter

The outlet and plug type used in Guinea-Bissau is C and in China are A, C and I. This is how they look like.

China

In China, outlets of type A, C and I are in use.

Type A

Type C

Type I

Guinea-Bissau

In Guinea-Bissau, outlets of type C are in use.

Type C