You Do Need power plug adapter while traveling from Grenada 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 Grenada is G. This is how they look like.

Grenada

In Grenada, outlets of type G are in use.

Type G

Guyana

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

Type A

Type B

Type D

Type G