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

Here is Why You Need An Adapter

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

South Korea

In South Korea, outlets of type F are in use.

Type F

United States Virgin Islands

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

Type A

Type B