How to stop leakage of mains adaptor
Switching supplies of this type usually have a capacitor between primary and secondary for EMI reasons: -



Notice C11 (220 pF) above the transformer at the top. This gives you the slight tingle and you should not consider replacing it unless you know what you are doing. You can double check things though.

You should measure the current with a meter to check that it is OK i.e. 1 mA or under does not pose a problem for anyone. A 10 nF capacitor at 50 Hz has 318 kohm impedance and from a 230 V AC supply could produce a current of about 0.7 mA. Anything significantly higher than this and I would worry about the supply. A 203 capacitor sounds like a 20 nF capacitor and this would potentially be able to source about 1.5 mA. It's probably still OK but if you are getting contradictory results between measurements and component values I'd consider replacing the device.

The other thing to do is check if the device should be earthed and convince yourself it is getting an earth via the plug. Chances are it doesn't require an earth but it's not unheard of things like this going wrong.

Play safe.