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