If you look at the numbers, you might conclude that your adapter takes
150W in to put out 50W. That's seriously overloading your 50W inverter.



There's no way it's *that* inneficient, even a linear power supply would
have far lower losses. More likely it draws about 65W, but the power factor
is probably quite low, so it pulls a lot more amps than the wattage would
suggest which may well have killed the little inverter.