How to get fast charging diagnostics information
AFAIK, no, it's not possible. Reasons :


Android only tells you the levels at which the device is considered to be charging normally or fast charging. This was based initially on current and now on power in watts. See Andrew's answer and also my answer there.
There are at least 5 proprietary fast charging technologies and obviously all details are not made public. Recognizing the device, the type of charging is a complex interplay between battery, charger and OS and is charging technology specific (whether current or voltage or a combination of both is used to charge fast) . The device may /may not recognize and notify if a different technology charger is used.
Even within the same technology, there can be variations; for example Qualcomm 2.0 increases current while Qualcomm 3.0 increases power (product of current and voltage).


IMO your mission would need you to have rooted devices, see the levels at which charging normally or rapidly is determined (first bullet point) and determine, if you can, from the system files what type of technology is used. It's easier to Google. To the best of my knowledge, there is no app that can help ( I may be wrong here, haven't updated myself)