You Do Need power plug adapter while traveling from Vietnam to United States of America (US) USA.

Here is Why You Need An Adapter

The outlet and plug type used in United States of America (US) USA are A and B and in Vietnam are A, B and C. This is how they look like.

Vietnam

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

Type A

Type B

Type C

United States of America (US) USA

In United States of America (US) USA, outlets of type A and B are in use.

Type A

Type B