Old Univolts liked to have a battery in the system for more stable voltage, so you may get strange results if you're measuring the output without a battery connected. I don't know what exactly the difference would be, I'm just going on the reports of people experienced with this.
I can say that I'm very happy with the performance of more modern 3-stage converters like my Powermax Boondocker, and no one seems to complain about Progressive Dynamics or Iota 3-stage converters.
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill