My M-140 laptop stopped charging and and after replacing the battery (it was old) I then replaced the internal power connector PCB assembly as I thought that was the problem.  I first measured the output of the charger, it was 19 volts, and my laptop seemed to work fine so I thought the PCB was bad and was stopping the battery from charging.  This did not fix the problem and I then googled more about this and found that a defective DS2501 chip in the power supply causes the laptop not to charge and to run at 1/2 speed.  I then bought a replacement genuine DELL charger that was much more expensive than others available.  This fixed the problem but unfortunately, something went wrong when I reassembled the laptop and I cannot turn the laptop on with the power switch unless I tape a small magnet adjacent to the lid closing sensor.  That is the subject of another post here. Since the purpose of the DS2501 is to prevent an owner from using an inexpensive replacement charger, and, according to what I recently read, an unshielded power cable causes the DS2501 chip to fail.