Suppose you plugged in your Phone/Tablet and it is not charging or charging very slowly etc. Problems might be; 1) The battery is dead and cannot be charged.

Suppose you plugged in your Phone/Tablet and it is not charging or charging very slowly etc. Problems might be; 1) The battery is dead and cannot be charged. 2) The cable is a non-charging one or internally damaged/dead or non-fastcharging or with limited fastcharging capability. 3) The charger is not capable enough to supply the max current that the device can use to charge itself. To troubleshoot the problem, first check the Voltage/Current specs for your device, make sure that the charger plug/battery can provide the same voltage but same or higher amount of current. Then use a USB power meter to see what is actually being drawn (or not) to figure out where and what the problem might be. One key point to note is that for fastcharging all the links in the chain i.e. charger, cable and device should support it.