So do you just have the one wall wart for all of these chargers?
Wall warts do fail in service...My Skil one died not so long back...If they are left charging after the battery pack is fully charged, they can and do overheat...Usually the primary fails..You can check this...Take your meter again, switch it to Ohms x10 range, range,now place the red and black probes together and the needle should go to the rightof the scale...Does it?
Now take the wall wart, make sure it is not connected to anything.
Connect the red and black probes to the two pins that would go into the wall outlet.....Does the meter read anything?
If not do the next step:
Change to the x100 range and try again...Does the meter read anything?
If not do the next step:
Change to the x1K range and try again...
Still nothing...? Bin it it's goosed.....