Dell specifications state support only for 180 W charger. If you have only Intel graphics and not also discrete Nvidia graphics, you might be able to use a lower-wattage Dell charger, though that would not be supported by Dell. If you have discrete Nvidia graphics, it would be safest to remain with the supported 180 W charger. Also, if you have a UHD display that will require more power than the lowest FHD display option. These are considerations when you contemplate reducing power supply.  
Now I am using Precision 7560 Lap top.Original DELL Supplied charger is 180.00W, but I would like to know minimum acceptable power input such as 140W or something without notification of low charging mode. Thank you for your support.
Minimum power requirement for Precision 7560