Compatibility summary
Your Spain plug may fit in Vietnam outlets, as both use at least one common plug type.
Plug comparison
Spain plug types: C F
Vietnam plug types: A C F
Both countries share at least one plug type (C F and A C F), so some plugs may work without an adapter. Check your appliance.
Voltage comparison
Spain: 230V, 50Hz
Vietnam: 220V, 50Hz
Voltage difference is within a range many devices tolerate; check your appliance label.