Charging from iMac thunderbolt port


Has anyone tried to use the thunderbolt ports on an iMac for charging?

I have a 2017 27-inch retina iMac. A picked up an apple thunderbolt to lightning cable, hoping to charge my iPad Pro faster than from the USB-3 ports. Strangely, even though the charging symbol turns on, the iPad essentially remains at the same charge level when plugged in either of the thunderbolt ports. Aren’t these also USB-C ports, and shouldn’t they have a higher power output than USB-3? This is really puzzling me.

I do not have an iMac but here is some information gleaned after researching fast charging batteries for an iPhone X.

It looks like the thunderbolt ports can deliver up to 15W when charging. USB 3 is, I believe, around 5W charging max.

I don’t believe the iMac can provide “fast charging” via USB-PD (power delivery) so the most recent devices supporting fast charging (iPhone 8/X, iPad Pro, etc,) will be limited to the port spec ratings.

Charge rate tends to decrease once a battery is above 50%.