Is there a cheap and easy means to evaluate iPhone chargers and cables? Is there an app for iPhone and iPad that will indicate charge voltage and current?  Is this information available to the user already by some means I am not aware of?  And without jailbreaking or some other hack?
The problem is that there's a number of third party Lightning cables and USB chargers that may not do exactly what they claim on the box and it would be great to be able to verify the claims.  Or there's the possibility that the box is long gone and there's a need to identify the capability of a cable or charger quickly.  It would be nice to get some idea on what a cable or charger can do without setting up some lengthy and involved timing of how long it takes to do a recharge.  It would also be nice to get some voltage and current data without some inline USB ammeter and voltmeter, as such meters can be easily misplaced when they are needed while an iPhone is always in my reach.
I found I can get some limited information about cables and chargers with my MacBook.  I can connect a cable between my iPhone and MacBook and see what System Information reports as voltage and current being supplied to the iPhone.  Because every USB port on an Apple computer is limited to 5 volts at 3 amps there's only three outcomes it tests.  Plug in cable and System Information shows data and power connection, this means cable has power and data connection.  Plug in cable, System Information shows nothing as if the cable is not connected, but iPhone is charging, means the cable has a power connection but no data connection.  Plug in cable, System Information shows nothing, and iPhone is not charging, means the cable is just broken.  I guess there is a fourth option.  Plug in cable and it starts a fire, then everybody dies, and people are sad.
I can do something similar with USB power bricks.  I can use a known good USB-C cable and plug USB power bricks into my MacBook and see what System Information reports about it.  Like with the cable test this gives little more than a pass/fail.  A MacBook doesn't &quot;speak&quot; USB-BC and so any such USB power brick will just show as providing 5 watts even if it is capable of more.  With USB-PD power supplies it will show the power supplied but not the voltage.  In many cases the power supplied indicates the voltage supplied.  12 watts or less means 5 volts.  More than 45 watts means 20 volts.  Other than that there can be some ambiguity on what the power supply is doing.
Searching the internet for an iPhone app that does what I'm looking for has proven difficult, perhaps as I don't know the right search terms.  That is assuming an app that provides the functions I'm looking for exists.
An app for macOS, or some other OS for a laptop with USB-C, might be helpful.  Such an app will not be much help in identifying USB-BC power supplies and cables but if there is something that can show what a USB-PD power supply is saying can be helpful.  The goal is to identify cables and power supplies in order to see how they will act with iPhones and other Apple devices with Lightning ports.  Something that can tell me what a USB-PD power supply can do is at least halfway to my goal.
The only thing I have found that consistently works is a USB-C power meter, such as this one from Satechi:
https://satechi.net/products/usb-c-power-meter?variant=31043692041
I have tested many combinations of chargers, adapters, etc. and this will give the correct information. I found that some combinations of chargers and adapters work differently with for example a MacBook Pro and an iPad Pro - so getting the reading off a MacBook Pro might not reflect what actually happens with an iPad for example. This has happened to me even though the iPad Pro on paper should support that same voltage/ampere - and probably does - but for some reason having an adapter in between the charger and the iPad Pro makes for a different scenario.