A Type B plug in Vietnam?
Yes — it seats, earth and all.
Vietnam's Type A and Type C and Type B sockets accept a Type B plug (US earthed (NEMA 5-15)). Both sides carry an earth, so grounded appliances keep their protection. The wall delivers 220 V at 50 Hz (198–242 V within tolerance) — if your device isn't rated for that (look for "100–240 V" on the brick), an adapter won't save it.
Grid facts verified against IEC World Plugs — Vietnam. Physical-fit verdicts derive from pin geometry and each socket standard's acceptance list — not safety advice.