Huh, that's interesting. I once worked for a laptop manufacturer, and the inverse problem (wifi only working when on battery) happened there -- it was an issue

Huh, that's interesting. I once worked for a laptop manufacturer, and the inverse problem (wifi only working when on battery) happened there -- it was an issue of high frequency electronic shielding off the power supplies. Something about how the modern auto-layout PCB software the ODM wanted to use had no way to take shielding issues into account and would want to lay traces in routes that an electrical engineer would never even consider. I can't think how the inverse problem would happen, though. Maybe it's software indeed.