Amps, watts, volts, cables - Help me understand

I’m hoping someone here can help me understand more about amps, watts (maybe volts) and the proper cables. I had initially intended to send this off to Anker, but I think the issue here is more fundamental.

As I have some longer flights coming up this summer (with no guarantee of power ports), I purchased an Anker Powercore 13000 battery—rated 3A and 47W. I gave it a full charge, and plugged it into my 2021 11” IPad Pro. It took 5 hours and 15 minutes to charge it from 34-100% (.2%/min). That seemed pretty slow, to me.

I let my iPad discharge a bit, and installed my Drok USB tester, and it only showed .94A. It also did this with a few other batteries I had—an Anker Powercore Fusion 5000 and an Anker Astro E1. They also only showed .94A. This was using two different USB-A to USB-C cables—both Anker Powerline.

I had assumed that the device would charge at whatever amperage is listed on the charger. Or is that incorrect?

I thought perhaps it was the batteries, so I tested with a bunch of wall chargers … a Scoche mini charger, Anker Power Port Mini, Anker Power Port 2, a desk lamp that has a USB charging port, two ‘generic’ USB wall charger outlets, and a Satechi USB hub. All of these are rated at 2.4 amps. On all of these I also only got .94A according to the Drok. I also tested with my partner’s iPad Air, and got the same results.

However, when I charge my iPad Mini 4, iPhone SE2 and iPhone 11 Pro via lightning cable, they all read (roughly) 2.1 amps.

Using the supplied Apple 20W charger, and the USB-C to USB-C cable, my iPad Pro charged from 64-92% in 40 minutes (.7%/min). I wasn’t able to test the amps with the Drok for this, as it’s only USB-A, but clearly it was much faster.

I’m a bit confused as to why the older lightning carries more amps, and not the newer USB-C. Or is the USB-A at the one end of the USB-C cable the bottle neck? To me, the 47W Anker battery should have charged faster than the 20W Apple charger, but it was much slower.

I don’t get it.