they're supposed to eat anything, and I've been feeding mine various pellet and flake foods for fish, but they never really respond well and dont swarm over them like they did when they found the shirakura food lol. i can tell they really like the ingredients in that one.
But the dwarf shrimp's foods are supposed to be blanched vegetables, algae disks, and other fish foods you can think of. vegetables are very important though. Plus the shrimp can survive for a long time in a tank (or bowl) just by eating various deposits, microfauna, algae, and even decaying plant material.