The USB accessory that you are connecting requires more power than the iPad alone can supply. This is often seen when connecting USB storage devices.
There are a number of ways to resolve this issue...
1) Ensure that the USB device has its own source of power. Some USB devices are battery powered - or can be directly connected to an accessory power adapter.
2) Connect both the USB device and the iPad (with your chosen Camera Adapter) to a powered USB Hub - the hub then provides power to the USB device over the USB connection.
3) Use the alternative (recommended) Apple Lightning to USB3 Camera Adapter:
https://store.apple.com/uk/xc/product/MK0W2ZM/A
This Camera Adapter, in addition to a Lightning plug to connect to the iPad, has both a USB 3.0 Type-A connection and a pass-through Lightning port - to which you connect your iPad Power Adapter. When connected, the Power Adapter will both charge the iPad and provide adequate power for the majority of USB “flash memory” storage devices.