You Do Need power plug adapter while traveling from Grenada to Saint Vincent and the Grenadines.

Here is Why You Need An Adapter

The outlet and plug type used in Saint Vincent and the Grenadines are A, B 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

Saint Vincent and the Grenadines

In Saint Vincent and the Grenadines, outlets of type A, B and G are in use.

Type A

Type B

Type G