I have bought a 12V laptop adapter for my inspiron 5570, the 220V adapter has output value of 19.5V 3.3A, the 12V one has either 19 or 20V both at 4A, I tried both settings but without success: says it's connected but doesn't charge.is there anything I can do to make it work?
You'll need to check to see if Dell has an adapter for DC power for your system - a third party adapter will not work. If there is no officially supported Dell adapter, the other option is a DC to AC inverter that will allow the use of the OEM AC adapter. Third party adapters will power the system, but the OEM adapter is required to charge the battery.
That's something you'll need to ask the manufacturer. Non-OEM AC adapters will usually power the system but not charge the battery; assuming the plug you have is correct, I'd expect the same of a DC power supply, unless it's either defective or somehow not compatible.