This happened when trying to use the charger for the second time. WARNING! This charger is clearly of questionable quality. If you must use it, place it well away from anything that could catch fire. I was extremely lucky to be in the garage when the charger first did this. I had carelessly placed it within about a foot of a gallon of model airplane fuel. If I had left it unattended and the charger had burst into flames, I am quite certain my I would be homeless right now.
UPDATE: One of the diodes was burnt out. That’s what was causing the problem. I went to RadioShack and bought a 25A 50V rectifier to replace the diodes. Surprisingly, the charger works fine again! I would suggest using 2 of the RadioShack rectifiers in parallel just to be safe. This should make the charger far less likely to self destruct in 55A jumpstart mode.