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