Don't worry, the shock won't do you any harm, the current is far too low.
One thing that can be a problem is that if you've got many SMPSes with the 0V rails connected together, the currents can add together, although you'd need many to get a harmful shock, the risk to electronic components is greater. This could be happening with your PC's SMPs but I suspect that the PC's 0V rail is connected to earth ground so it won't be a problem.
If it's a problem, try connecting the 0V to earth ground with a 100nF capacitor or powering the supply from an isolation transformer. The capacitor will bypass the current to earth reducing the voltage to a safe level (both for you and semiconductors) and an isolation transformer will isolate the incoming mains supply from earth. You shouldn't need to do both, either the isolation transformer or capacitor will do, depending on which is more convenient.
Note that transformer's VA rating might need be much higher than that of the SMPS's power rating because will have a poor power factor unless it has active PFC.