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

Here is Why You Need An Adapter

The outlet and plug type used in Vietnam are A, B and C and in Bangladesh are A, C, D, G and K. This is how they look like.

Bangladesh

In Bangladesh, outlets of type A, C, D, G and K are in use.

Type A

Type C

Type D

Type G

Type K

Vietnam

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

Type A

Type B

Type C