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

Here is Why You Need An Adapter

The outlet and plug type used in Guyana are A, B, D and G 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

Guyana

In Guyana, outlets of type A, B, D and G are in use.

Type A

Type B

Type D

Type G