Charging cables are accumulated over time of buying new phones and other tech that uses the same size port whether it is USB-C or MicroUSB. The charging cable that comes with a phone might not have the same power as the cable that comes with a set of bluetooth headphones. Also another factor could be the brick that connects the cable to the outlet. The app, Ampere, can be used to give an estimate to how fast your phone would charge with your charging cable and power brick.
The easiest way of testing charging cables is by plugging them in and observing the max mA readout value and compare it with a variety of different cables. The same can be done with your power bricks.
The Pro version has a setting enabling a persistent notification which can make it easy to monitor how using intensive apps like Netflix or games put a strain on the phones battery or charging speed. It also removes the ads in the app. See below a few screens of the app while unplugged, charging, and different settings.