Check the healthyness of the capacitors provided in its filter ckt.Also check the harmonic s content in the DC out put by ossilloscope.Choosing the values of Propercapacitor in the filter circuits . Defects may be rectified.

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One thing more... on many supplies, the mains noise filtering use two high voltage capacitors (typical 5nF/5kV). Each from live and from neutral to the earth pin. But if such filter is in your lenovo supply and the earth pin is not connected, then the voltage on the 'earth' on the laptop's ground will be divided by the two capacitors - so you may have 115vAV on the laptop - independent if you swap live and neutral. Just my cent.

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Hi. Laptop manufacturer may use the sense pin (resistor) to sense a specific supply. I.e. same brand may provide big/small power supplies with same plug!. Then laptop can detect if correct power supply is connected - and if the resistor represent a too weak psu, then the laptop will come with a warning and perform lower.
Wrt 50Hz-shock, try swap live(phase) and neutral(return) to feel if the shocking become less? If so - then it can be the cross capacitor as mentioned earlier -or leaking debris across the transformer barrier -or worse- the insulation in the switching transformer/barrier is degrated due to exposure to ESD voltages (lightening) when it was in use. A short high peak between primary and secondary side may toast the capacitor and/or the insulation barrier - without making the supply non-functional! That can be tested by proper high voltage testing equiment. But I doubt the cost of a new powersupply can justify many hours of reserach in finding the cause in a broken laptop supply. But interesting if there is an easy way to save it.

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Paris,
Our wall outlet is 230V AC, Line to earth showing 230V & Neutral to earth showing 0V..

What modification you suggest?

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Humberto,
I was also exclaimed.......Lol

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Yogesh, can you please tell me what is the A.C voltage level at the wall outlet you used to power and test this power supply, if you measure a) across the phase and ground conductors and b) across phase and neutral conductors? (With the outlet free of course, i.e. nothing connected to it).
I am asking you that because interchanging Live and Neutral MUST have an effect. Here is why:
Having as reference the above schematic (which doesn't differ from the most cheap designs), this noise suppression capacitor is always connected as shown therein.
It is clear therefore that one end of it is connected to the minus side of the bulk capacitor (primary circuit ground), while the other end of that cap is connected to the secondary ground (ground to ground coupling).
Therefore, under normal conditions, if the Live is connected so that it appears on the plus side of the bulk capacitor, this means that the primary side ground is effectively grounded through the neutral conductor. In turn, the secondary ground circuit will be safe.
These cheap designs use the circuit ground as safety ground, but this is absolutely wrong. This is exactly what happens in your case and ideally needs a modification.

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Thanks! for your comment...I think your first point should work.

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