Don't have my brick anymore, lost it, but I use my usb ports on my pc.
That can be be problem. USB Ports on computers can be inconsistent when it comes to charging. This is why even Apple says to use the brick
Basically charging issues come down to one of several things in no particular order)
1. Debris in port or damage to port - broken pins, short circuit (what's that brush made of, if it's not ESD safe material you could have damaged the port via static shock)
2. Bad cable. Either damaged, including pulls that dislocate the wires and typically cause wrinkling in the cover materials, or third party cables are most likely here
3. Bad wall plug. Damaged, third party or in the case of an iPad using the wrong wattage, which works but hella slow and don't try to use it at the same time
4. Damaged or poor functioning electrical source. Bad wiring in wall jack, low wattage USB port on comuputer. A common issue is using the front port on a pc tower as it is almost never full strength. Same with USBs on laptops where it's located on the side opposite the power intake.
5. Consumed battery
6. Bad internal logic board (for this you will typically see other issues like constant random shut downs, graphical anomalies like colored screens randomly appearing and so on)
7. Corrupt software causing something to use as much or even more battery than what is coming in.