What is the exact amperage provided to the phone during dual charging?

This looks like a great idea, and definitely fills a need. I have been using an apple watch/iPhone 6s+ combo stand that I designed and printed on my 3D printer. With each having an individual power supply, charging is pretty quick, which is handy on nights where I'm not in bed for long. I am concerned as to how much power drop will exist with one supply, possibly increasing the charging time for both devices.

Thanks!

Belkin Valet Charge Dock for Apple Watch + iPhone

Belkin Valet Charge Dock for Apple Watch + iPhone

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