Presumably the travel charger was designed to be compatable with Dell laptops (i.e. it provided the serialised ident signal on the centre pin to indicate it was a "Genuine Dell Charger") otherwise it will only power the laptop itself, merely avoiding draining the battery (which is better than nothing at all).
All that's happened is that the problem of accepting 12 to 15 volt DC power (which could have been addressed by the power management in the laptop itself) has been worked around by some clever smpsu technology incorporated into the travel charger alongside of the more standard universal 100 to 240 mains smpsu part of the charger. It's a damn fine travel charger, kudos to the manufacturer! :-)