Compatibility summary
Your Australia plug may fit in Tonga outlets, as both use at least one common plug type.
Plug comparison
Australia plug types: I
Tonga plug types: I
Both countries share at least one plug type (I and I), so some plugs may work without an adapter. Check your appliance.
Voltage comparison
Australia: 230V, 50Hz
Tonga: 240V, 50Hz
Voltage difference is within a range many devices tolerate; check your appliance label.