The table below summarises the plug types, voltage and frequency of electrical current in both Singapore and Korea, North.
|Frequency of electrical current||50Hz||50Hz|
Singapore uses Plug Type G.
You will need this adaptor:
Socket Type G
(Singapore) to Plug Type C
The voltages found in Singapore (230V) and Korea, North (220V) are not exactly the same, but the difference is tolerable, so you should not need a transformer.
The frequency found in Singapore and Korea, North is exactly the same (50Hz). Timing devices and appliances that use motors will function as expected under this frequency.