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

Here is Why You Need An Adapter

The outlet and plug type used in Japan are A and B and in Saint Vincent and the Grenadines are A, B and G. This is how they look like.

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

Japan

In Japan, outlets of type A and B are in use.

Type A

Type B