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

Brunei

In Brunei, 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