You Do Need power plug adapter while traveling from United States Virgin Islands to Swaziland.

Here is Why You Need An Adapter

The outlet and plug type used in Swaziland is M and in United States Virgin Islands are A and B. This is how they look like.

United States Virgin Islands

In United States Virgin Islands, outlets of type A and B are in use.

Type A

Type B

Swaziland

In Swaziland, outlets of type M are in use.

Type M