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

Here is Why You Need An Adapter

The outlet and plug type used in Vietnam are A, B and C and in Israel are C and H. This is how they look like.

Israel

In Israel, outlets of type C and H are in use.

Type C

Type H

Vietnam

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

Type A

Type B

Type C