Why won't my iPad Pro charge from a USB-C hub?

Do you experience any charging issues when connecting your iPad directly to its USB-C Power Adapter?

Not all USB-C hubs work well with iPad and iPadOS. When choosing a USB-C hub, ensure that its specifications explicitly state compatibility with iPad - as some use internal chip-sets that are not fully supported by iPad.

There are many USB Hubs that have a USB-C connection for iPad plus a USB-C PD (Power Delivery) pass-through power connector to which you can connect your USB-C Power Adapter - along with the hub itself incorporating a combination of additional USB-C ports, USB 2.0/3.1 Type-A ports, Ethernet LAN, HDMI, VGA, SD and microSD card-readers - in in some cases, a 3.5mm analog audio/headphone jack.

Perhaps consider Kingston, Anker, Hyperdrive and Satechi - although there are many others from which to choose. A Google Search for USB-C Hubs compatible with iPad will find a number of articles and recommendations. 

When using a USB-C hub, ensure that your Power Adapter is sufficiently powerful to both charge the iPad and power connected peripherals. A USB-C multiport hub may typically require 10W power just to run its own electronics; connected USB devices (external storage, keyboard, mouse etc) also draw additional power from the source. If the connected load exceeds the available supply, the iPad may not charge - or may charge at a substantially slower rate. In extremis, both the iPad and Power Adapter will share the connected load - and the iPad may actually discharge its battery to make-up the shortfall in available power from a connected Power Adapter.

You should note that while Apple devices generally support USB PD, they do not support other charging standards - such as QC (Quick Charge).

The hub and any connected accessories require power. You must consider your "power budget" such that the connected power source has adequate capacity to provide power for the hub, connected accessories and the iPad.

A USB-C will typically require ~10W just for its own power needs - plus your iPad will require at least 12W to reliably charge. As such, a Power Adapter that support USB PD (Power Delivery), rated at 20-30W, is the realistic minimum.

Many third-party Power Adapters do not support USB PD. Apple devices do not support other proprietary charging standards - such as QC (Quick Charge). When connected to USB-C power sources that do not support USB PD, your iPad will default to standard 5V charging at a maximum of 2.4A (i.e. 12W).