I don't know about your "converter", but my Iota DLS-55 (converts 120VAC to 12VDC at up to 55 amps) makes an impressive spark/pop-sound when you first plug it in to an AC outlet. Seems that there is a huge inrush of current to capacitors in its circuit. This is not an AC-transformer-based charger, rather an efficient switching-mode circuit, presumably the input part of the circuit is diodes and large filter caps to turn the AC into DC?
Perhaps you can set up a way to slow-start the "converter". E.g., add a switch that disconnects it from the AC supply, but bypass that switch with a resistor chosen to limit the inrush current to just a few amps. E.g., a 20-ohm resistor would limit it to 6 amps even if the converter side is a dead short. Also would help if you can disconnect the load (battery) from the converter. Then plug in with both switches off, after a few seconds turn AC side on, then DC side. That way the resistor does not need to be huge (in power handling capability) since the converter will be running in "low idle" after the initial rush and until the load is connected.
Or, instead of a resistor, use a light bulb, e.g., a 100W incandescent bulb (for 120VAC) would limit the current to about 1 amp, but allow more than that in the first instant before it heats up. Sure cheaper than a large resistor...