If you are copying the photos onto the SD card yourself then you need to create a DCIM directory off the root of the card with the photos underneath it, and the photo filenames need to be exactly 8 characters long (no spaces) plus the file extension i.e. in a similar format as if a camera had created/written them on the card
I have 3 USB flash drives - 512MB (old), 1GB (newer) & 4GB (newest). Only the 512GB draws to much power. Get a new one.
Here's how I do it.
Plug the USB flash drive into your computer & create a new folder titled DCIM. Then put your movie/photo files into the folder. The files must have a filename with exactly 8 characters long (no spaces) plus the file extension (i.e., my-movie.mov; DSCN0164.jpg).
Now plug the flash drive into the iPad using the camera connection kit. Open the Photos app, the movie/photo files should appear & you can import. (You can not export using the camera connection kit.)
another element with the flash drives, if it's a kingston or sandisk (and there may be others) that have bundled software when that software tries to run it triggers the 'too much power' warning.
also if the flash drive has any flashy LED lights they will draw too much as well. I experimented with some of mine and had a 50/50 success rate.
Using the SD card is definitely the best way. USB can work, you just need some tweaking