Yeah, it all depends on what type of powered USB hub...
This is the primary factor. Each USB port on a computer is rated based on a specification, but "hubs" that we add split the power from that single computer port across all the connected devices on the hub. POWERED hubs (that have a USB cable to connect to the computer, AND a dedicated power cord from an ac adapter) will have their own strategy and specification. Not all powered hubs provide full power output on every port, many/most will allow full power on one or more but not all. The specifications included with the hub would indicate total power output, and you'd have to do the math on how that translates to the intended load/connected devices being powered.
Hypothetically, if using a powered usb hub and a USB 2/3 interface, you should be able to connect say a single thumbdrive and maybe a keyboard/mouse without drawing too much power. Interface plus a portable usb hard drive (like a 1/2TB usb drive) will probably be the max power draw allowed.
While I understand the relatively low power needs for audio interfaces, and convenience of only having one cord for data and power over usb, I've always wondered why all audio interfaces don't typically come with an ac adapter (*). That extra duty of internal power management by the interface seems like complexity being added that isn't required.
(*) I wonder if part of the strategy is noise shielding... relying more on the computer's design to reduce interference than trying to bake that into a budget interface... (?) Adding a power cable from the wall definitely increases the odds of introducing some noise from the ac adapter and/or power cabling.
