Patrick provided a great link. It confirms what I suspected all along, but had not found confirmation anywhere. The link confirms this: “When used to connect Thunderbolt 3 devices to a Thunderbolt or Thunderbolt 2 Mac, it must be a self-powered device. Bus-powered devices connected directly to that Apple adapter are not supported.” This is why my TB3 to TB2 adapter did not power up the digital converter. I will say that if your bus-powered device has a power plug, then it should work when plugged into a power source.
BTW, my Canopus ADVC-110 does have a power jack; it just does not come with a power cord.
Also, a Firewire 800, when plugged into a FW800 to TB2 adapter DOES work.
Thanks for the link Patrick!