Re: 5v/12v ring
More efficient step-down instead of 20 cheap/nasty/dangerous transformers around the house? Not sure their efficiency - a cursory Google suggests 60-70%.
Then there's the dodgy versions. Even the supposedly good ones (Anker as an example) exhibit some of the symptoms of cheaper chargers (I've got "flicker" on mine, leaking noise from the AC meaning the touchscreen on devices is erratic) which is one of the least problematic issues.
A cool (nerdy) comparison of how they're performing is here:
I wouldn't mind a chunky certified transformer in one place doing this in a safer manner. Wouldn't say it should be retrofitted, but new house builds could certainly benefit from it.