How to charge APP 3

I just spent close to $300 for APP 3 (incl tax), brought them home to charge them, and there’s this white piece of plastic down the middle of USB-C charger hole. The online instructions say I need to have a special power adapter. Naturally, I look in the very expensive cardboard box with the plastic liner to find mine. I don’t see one. I’m embarrassed, please be patient, but what is this super-secret special adapter? I wanted to plug in my AirPods tonight and charge them so I could work immediately. What good is this device if I can’t charge it? I feel both dumb and annoyed. Thanks for your help!