So after I got the warranty order in, I then got a message with a return label attachment. It's using USPS ground return service and has a barcode for the RMA as well as a USPS tracking number. I still have the box that it shipped in with the UN3480 info printed on one side. I suppose just wrapping the defective power pack in bubble wrap and a few air packets and it doesn't move much. I figure that would be good enough. I'm saving the original package and I'm not returning the USB-C/USB-A cable that came with it.
Don't know if they're going to wait until they get it before the send the replacement, or if they'll send it out and charge me if they don't get the return.
The last time I had to return anything, ZAGG said I needed to wait for the replacement and to use the shipping box to send the defective item to them, or face the possibility of being charged for it if they didn't get it within 60 days.