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I want to try and charge a MBP off the iPad Pro!

It probably won't though I have been screwed a couple times when my USB power brick tried to charge itself off my phone because I hadn't pushed the button to switch the port from drawing power to delivering power.

Is there some sort of protocol in USB-C for two devices with batteries to negotiate which should charge the other. Though I imagine the iPad could just refuse to deliver the high power states/not have the circuitry.

It works for Macbook to Macbook charging, so why wouldn't it work with the iPad?

Note that your device doesn't have to provide the requested power if it is unable to, it can provide less.

Doesn't the Macbook require a certain minimum power to be available before it will start trying to charge though. IE if I plug it into an old .5A USB charger would it try to charge off the 2.5W? That's most of what I meant when I was talking about providing enough power.

It charges quite happily off the 3W max which is standard on most non-power-delivery USB-C ports (inc Apple's, iirc)

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