It charges my Sony WF-1000XM3 earphones without a problem.
#2 How to recharge this 20000 pd portable charger?
It is recommended to charge the 20000 PD power bank with a PD supported USB-C wall charger(such as Apple's 18W/29W/61W/87W adapter) along with the included USB-C to USB-C cable which will be in around 3 hours.If you don't have a PD charger, you can contact the buyer to purchase 30W or 60W PD chargers at a preferential price.
#3 Has this stopped working for macbooks when people upgrade past mac os x 10.5.1? if so, is there a new version to deal with that?
Works great with my 2016 MacBook Pro 15" running Catalina Version 10.15.6
#4 How about a simple statement of the watt hour capacity? The 20,000 mAH capacity is meaningless without knowing the voltage.
It's stated as the back of the device. Battery Capacity: 20000mAh/72.6Wh. Minimum Capacity: 19400mAh/70.4Wh. Hope it helps you make a decision. I'm very happy with the powerbank overall, it can charge my ipad almost twice and it's really fast.
RAVPower
Owner manual PDF of RAVPower RP-PB201 20000mAh PD Pioneer 60W 2-Port Power Bank.