A pretty weld is not an indicator that it is a sound weld (strong as the base material or more). Like my old welding instructor said over 60 years ago, pretty is not where the strength lies. He concentrated on full penetration from the bottom of the material to the top. What is over the top does not add more strength. At my age pretty went away with the arthritis and neuropathy problems; but, I still concentrate on penetration. No matter how you cut it 20A 120V will only produce so many amps at the stinger. It takes amps to get penetration. I trust my life to penetration and soundness. I refuse to get into the on going ballyhoo, only to say, I use a 225A DC machine fed with 50A 240V and stick weld exclusively.
Ron