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.
Zero Gravitas — 2017 Flying Cloud 26U | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
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