You Do Need power plug adapter while traveling from Vietnam to Puerto Rico.

Here is Why You Need An Adapter

The outlet and plug type used in Puerto Rico 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

Puerto Rico

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

Type A

Type B