I've built a Faraday cage, as best as I could considering all the input and output lines. No help. What proved it was that I wired the adapter directly to a 12v battery. If it was propagating over the air, then I would have had the same interference.

The block diagram is an actual adapter. All of the Chinese built adapters I've disassembled have this layout, with no filter at all on the 12V side. LM7805 can't handle enough current. I need 4A to drive two ports.