can tell me if their phone does not always connect to their PC
Lemme try and throw some clear light on this issue as many things in play.
I would be very surprised if it is the actual cables as there are a bunch of variables.
Many USB ports especially on laptops are not powered, they only have data lines. Often just one of the two or three ports will actually be powered internally.
Many USB ports especially on laptops will have power but able to be turned off/on according to some settings.
Many USB ports especially on laptops will have power turned off if the battery is getting low or the laptop is running on battery and not plugged into the mains.
Many USB ports especially on laptops deliver differing amounts of current. The USB protocol 2 is rated at a max of 500mA and USB 3 at 900mA. Either or both of those can be throttled back and/or shut off on some PCs, laptops especially.
Many walwart power supplies are apple tweaked to require a signal from the device to let the flow begin. Dumb idea but hey, it's apple OK. Without that signal nothing happens and that's why you will often see two USB ports on a walwart and one will have a tiny "A" alongside it. That port will not deliver current unless an apply-type signal is present whereas the other port is "normal."
Very, very unlikely to be the cable -- unless it is a faulty cable..