USB-C Charging Speeds / Charger Outputs I own a 2016 Macbook (with the USB-C charging) - at the time and in response to all of the reports of poor cables and poor chargers, I bought a meter so I could see what the throughput of my cables/chargers was. However, having run some tests I'm now not sure what to consider normal / what is harmless to the battery. 

For all tests I used an original Apple C-C cable - though was able to replicate with two third party cables I own.

I have the original Apple block charging at 14.3 V / 1.99 A and a third party block that charges the same.

Another third party block which advertises USB PD and 3 A is currently charging at 20 V / 1.43 A

I've done some research online but I can't find any articles that indicate what a normal USB PD output is relative to the devices that connect to it and would appreciate any guidance / assistance. 

TL;DR: Have Apple charger which charges at one voltage/amperage. Bought several others advertised at PD which are higher voltage, lower amperage. Not sure what is 'safe', or 'fast', or does least overall damage to battery.
A good Multimeter is fantastic - I use one all the time - however it's not clear from your question just how you're using a Multimeter to take your measurements? 

Considering we're talking about a fairly recent model MacBook Pro, I suspect you haven't opened it up to take these measurements. Instead, I recommend you download and install coconutBattery1. It provides a whole heap of information that you'll find useful, and from memory includes both Discharging and Charging measurements in watts!

Some thoughts

It's not clear from your question why you're investigating all this? Unless you've actually got a problem you're trying to address, using the charger that came with your MBP should be perfectly fine. Also, in relation to you not finding any articles that indicate what a normal USB PD output is relative to the devices they connect to, that's because PD stands for Power Delivery and most of these devices are just designed to allow the power travel through them from the charger to the device being charged. 

In other words, you can use a hub with a USB-C PD port with a 2017 MacBook Pro and also use it with a HP Elitebook and the voltage/watts will differ, depending on the device and charger.

1 I am not affiliated with coconutBattery in any way.