Schematic is here:
I will break down the schematic.
The two input ports are data and power.
The data port is connected to the data lines TX/RX for USB3, and USB D+ and D- for USB2. The voltage lines are connected through a rectifier which is a 'one-way' path to the Oak.
The power port also goes through a rectifier and the data pins are not connected to the Oak. It has the sense pins tied to 5.1K resistors which tell the USB connected to it that it wants 5V power up to 2.1A, but this is not guaranteed since it is based on whatever is connected to it. For instance if you plug it into the USB OTG port of a Pi Zero it will almost certainly crash it but a most decent 'charger' bricks with a USB-A output socket will most likely give at least 1A if used with high-quality USB cable less than 2 meters long. Any power supplied via USB-C connector that conforms to the USB-C standards will supply the needed power if used with a standards compliant USB-C cable.
This means you can use anything (compliant) with a USB-C port to connect to the power port and the data port will be isolated so that you can use whatever you like for a host. If you don't have USB-C you can use a power bank or 'charger' that is rated for at least 1A / 5W (preferably 2A / 10W) with a USB-A port to provide the power.
Always connect the 'power' first before connected the host to the 'data'.