Your controller can be powered a number of different ways when connected to a MIDI Expander. The first is to connect the Expander's POWER input to a power outlet via a USB cable and USB power adapter. The second is to connect the Expander's POWER input to a computer's USB port. The third way you can power your controller is to have the controller connected to a computer via its main USB port while it is also connected to the Expander via the Expander port (this method will not work with QuNeo as it only has one port, but will work with SoftStep and 12 Step as they have a separate Expander port).
Any of these methods will be able to reliably power your controller and Expander.