A lot of the time, what these “multi-port” chargers do is they have one port hooked up to the fancy multi-voltage converter, and then all the other ports are ganged up to one 5v converter. Doing anything fancier would cost just as much as two power supplies. If two beefier-than-a-phone-charger power supplies is what you want, there isn’t really a better solution than buying two separate power supplies.