Our iPhone 8s and iPad are pretty picky about the voltage drop along a charging cable. Our bedside clock has a USB in, to power it, and a USB out. I haven't bothered or needed to use the USB out, but last night one of our phones was low and I tried to charge it via the USB out; it didn't work. At a guess the voltage out, coupled with voltage drop along the cable was too much. I then had a thought: recently I bought a couple of spare wireless charging pads. I plugged one of the pads in to the clock and popped my iPhone onto the pad; charging started. So this suggests that wireless charging is far less picky in terms of USB voltage. I also tried a USB inline voltage meter between the USB out and the pad. which indicated 4.75V - far too low a voltage for my iPhone via direct cable. In fact the drop across the meter to my iPhone will not charge direct from a standard Apple wall charger. No guarantees that this will be the same for other iPhones or perhaps different models of wireless charging pad, but it is useful to know.