I’ve actually run a few of these tests myself. And yes, I get <4VDC out of a usb port on the charger. But not from the 5V pin (Which actually outputs ~7VDC) the <4VDC is the signal pin, which tells the phone it is plugged into an authorized charger. I’ve got 5 different portable battery packs for my phone. 1 is solar, but the panel on it is maybe 1W output.