I would test it. I looked at those converters for my mini phev kit that supplements the charging system and many are not adjustable. They also roll back or cut out when they get a certain temp. I ultimately went to 2 deep cycle batteries, an inverter and a mean well power supply. First a 150 watt then a 350 watt set to 14 volts. I know its full of losses and inefficiencies, but it works and I already had the parts laying around.
Still, even pushing 30 amps there are situation where its not enough and the converter has to take a break to cool down. Of course this is on a 2010 insight.
Maybe an older car like a metro uses less power?
If you are passing through Richmond you can take my rig for a test.