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