Is it possible to power the S30 during its use with an external source (power bank) via the USB-C connector to have more usage time during a night session?
Yes, at least the S50. I assume the same thing is true for the S30.
Yes it is, I use a powerbank on both my S50 and S30 with no problem.
Of course, as long as it's a USB cable with a Type-C connector, it will work.
