Richard_432 wrote:
Thanks for all the helpful replies. Yes that Belkin 11 in 1 dock is the one that I have. Would I perhaps be safer to just plug my 20W iPad USB C power adapter into that dock? Or would that then be under powered for my iPad Air?
The Belkin dock specifications clearly states that the dock itself requires 15W for its own power needs. The dock contains multiple interfaces, (VGA, LAN, DisplayPort, HDMI, SD and USB2.0/3.0) all of which require power in their own right. In addition, connected USB devices all draw power as well, some having greater power requirements than others.
The Belkin hub supports up to 85W pass-though to the connected host, via the pigtail USB-C connection, using USB PD. As such, while your 20W USB-C Power Adapter can be used with your Belkin dock, its overall power output is inadequate to both power the dock and charge the iPad - let alone provide power to connected devices.
As outlined in my initial reply, you need to consider your overall Power Budget…
Your iPad, when charging at its peak charging rate, requires ~20W. Your Belkin dock requires 15W for its own electronics. USB devices connected to the dock also require power. If the Power Adapter cannot provide sufficient power for the dock and connected USB devices, your iPad will share the load - providing limited power from its internal battery to cover the shortfall from externally supplied power. You should note that, for practical purposes, the dock is unlikely to be capable of supplying maximum power to all of its ports at the same time.
Each connected USB device may potentially draw up to ~12W; for USB devices that are not attempting to charge their own internal battery, 5W is a reasonable estimate. For the Belkin dock, with three downstream USB ports, 36W should provide a realistic worst-case requirement.
For your setup, with the iPad connected as host computer, your USB PD Power Adapter will ideally need to supply ~70W (35W minimum) - these being within the dock’s quoted overall 100W capability. For a connected PC or Mac, having greater power needs, a USB PD Power Adapter with a greater power output might be more useful - remembering that the docks maximum power handling is itself limited to 100W.
For this to work, your connected Power Adapter must support USB PD (Power Delivery). The power source (Power Adapter), dock/hub and connected host device all support USB PD - and negotiate the highest mutually supported PD Power Profile - of which there are many. The dock has its own internal power electronics, that provides power to connected USB devices at the standard 5V USB bus voltage.