> How is the regular guy supposed to figure out if a USB device is OK or not?

If you are not absolutely sure it's OK, then it's not. Pack your own chargers, use a "USB condom" or a power-only cable. If the charger has a cable that can't be removed, use it to charge a trusted battery, then charge your phone from it. Don't trust any smart battery, BTW.

Journalist covering summits like this are not regular guys and should receive opsec training before any such assignment.

When working on the Brazilian electronic ballot, I had two computers: one that was connected to the corporate network where I could read and write e-mails, and another I could manage (so I could run Visual Studio's debugger), that was on a completely different network, in front and behind some of the most aggressive firewalls I've ever seen.