My iPad pro wifi cellular 10.5 inch fails to recognize USB flash drives connected using Apple Lightning to USB 3.0 Camera Adapter informing that Excessive power is required Please advise the technical specs of the required adapter

When using the Lightning to USB3 Camera Adapter with USB storage devices, you must also connect your Power Adapter to the pass-through Lightning port of the Adapter. Your USB Power Adapter must be rated 12W or greater.

Most USB storage devices require more more power than the iPad can provide. In some cases, if the USB storage device does not have its own power source, it may even be necessary to connect via a powered USB Hub.

USB Power Adapters are not all created equally. A standard “5V” USB Power Adapter of 12W or greater is required - or a USB PD (Power Delivery) Power Adapter, these typically being rated 18W or greater. Some third-party Power Adapters do not comply with the USB PD specification (as supported by Apple devices), but instead are designed to operate using the competing QC (Quick Charge) standard used by many Android devices. Apple devices do not support USB QC.

Your mention of a 15W Power Adapter suggests that you are not using an Apple OEM Power Adapter.

It is certainly possible that your Lightning to USB3 Camera Adapter either has fault, or has been damaged by a non-compliant Power Adapter. As such, substitution of both the Camera Adapter and Power Adapter are a reasonable suggestion when troubleshooting.