I’ve got to say that the usefulness of the OP 's phone is a worry. My phone is still a long way off (ordered Sept 2019), which is good as it will allow for further development, bad for the length of time between order and delivery however.
I think that the phone is now over $1000 to order? Mine was $699. At either price point I’d be looking to use this as my main phone. I am not filled with confidence by this owner’s experience, but, as Mick Jagger said, time is on my side. Its still not great.
Does this mean that the adjustments with the vol+ and vol- buttons is bad calibrated?
I think (as non-expert) that any replacement for the original Librem 5 power supply should not go out of this main power controller range, coding/protocol range actually (probably not easy to be found, less protocols supported is better option toward solution, as PD2.0 only Type-C port not easy to find either):
For example (and although I don’t have one) Aliexpress offers this power supply, but which Infineon CoolMOS™ chip is built in I cannot even guess, yet at least narrow down which kind of PD technology/controller it supports.
And, I’d like to make this post list short, simply try (should be easier to find): “Apple’s new 18W USB-C PD, A1695 AC adapter”. Just my few thoughts, adding that preferably any power supply controller inside of this replacement should be USB-IF approved, at least, yet not confirming any kind of on my wish list compatibility with minimum requirement you are looking into, all while your original power supply lost.
Also, only 5V chargers should (at least temporarily) serve the purpose as well, therefore: https://www.powercubes.eu/en/product/usbcube-original-usb-ac-black/ (I’d expect it supports dedicated charging port only on it, known as DCP coding, but don’t know for real). DCP (BC1.2) related info: “It is allowed to draw more than 1.5A from this standard, if the connectors are rated for it and the power supply can deliver.”
Edit: PD3.0 only (without other protocols involved) power supply (actually hub) that I know of (involves one port only) is PD/HUB Type-C port (18W) from this device:
That ZDSHB01 device is working well with Librem 5 is confirmed here: https://source.puri.sm/Librem5/firmware-tps6598x-nonfree/-/blob/master/dp-alt-mode-adapters.org.
P.S. Just do not think that middle Type-C port (30W) is the one to be used with Librem 5, yet and if of any interest, I can still upload this port charging protocols as well?
Somewhat not recommended up to this Amazon review: “The charger crashes on voltage-to-voltage transitions.”
That is why i ONLY recommend usb-if verified charger, so maybe this charger it has a fake usb-if certification or errata. A genuine USB PD charger is commonly expensive.
The Librem 5 charger it a genuine product to meaning not a cheap charger and cable, but it support only low voltage so not compat with Libre 14.
Thanks buzz.
I’m not sure if it really works. I tried to set 10% but I’m not sure the hear a change. Anyway, thank you very much for help. 
Can you try with some higher value say, 50% or 75%?
It works. Now a deaf person can hear it. Thank you very much buzz
of course it does 
Just be careful not to crank the volume way too high. I use it upto 300% on my Thinkpad with Manjaro. But since we are dealing with phone speakers so not sure what number can be considered as “too high”.
I think you are right buzz. Probably set a value between 50 and 75% as you suggested is enough