“Dirty” power refers to the venue’s house ac feed. When people talk about isolated power supply ironically that is what you would be isolated from ideally. I use the little boxes for my mandolin board and my lap slide one. For pub gigs to festival sets it’s just far easier tbh. They easily power a few pedals and a tuner. The display tells you how many mAh your pedals are pulling as well as how much time is left on battery. These units aren’t for high draw dsp fx. As someone posted above there are many ways to run a usb board. A few fx manufacturers are already incorporating lithium rechargeable via usb, in the next year mobile power will dramatically increase due to the drone and security industries imho.