I have two GAN chargers - an 18w and the two port 60w. I use them Both with usb c to charge my Lenovo laptop - even the little one does a good enough job.
I also use a usb c to lightning cable to charge my iPad and iPhone XR. Recently the charging rate has fallen off a click for both devices and both chargers. I’m pretty sure I’ve tried alternative cables and nothing seems to work. Any idea why?
Really weird. I have a GAN 18w Charger and i haven’t noticed any dip in charging time…
I also have a 60w gan Charger but i haven’t had it very long yet.
Likewise… I use the Powerport Atom III (2 Ports) GaN charger daily, and not seeing any issues with charging or powering my Lenovo laptop
How do you say it’s slowed down? Do you use USB Charge meter to measure power / Ampere?
Did you try different outlets? Maybe the issue is the outlet or maybe it wasn’t plugged all the way in
My basic metric is that iPhone should charge to 50% in half an hour. Sometimes only getting 20%. In the iPad my usage is faster than charging.
Is there a way to check amps coming in on the iPhone?
You’d need a USB power meter to check voltage and amperage. In this case one that supports USB-C. This is an inexpensive and easy to use one.
With the iPhone the amperage won’t be that high. You mainly want to make sure it is jumping from 5V to 9V after 5-10 seconds. That indicates fast charging is active. The current (amps) will continue to decrease as the battery charges up. Whether the phone is asleep or active will also affect the current.
I tried but did not add these details… Your answer nails it 
… just perfect!!