When mine are in molt, I up the protein, and calcium. I switch to a show feed, and a couple times a week feed them cat foot, canned mackerel, eggs with the eggshell in it, and extra mealworms. It seems to help them a lot. That's usually the only time I switch them from their normal feed.
Years ago, I bought a pullet that had very poor feather quality. I got her looking good, and then she went into molt. That poor little hen lost every feather overnight, and didn't have a lot of energy. She looked pathetic, and quit laying. I was looking into my SOP birds at the time, so I got a bag of show feed. I fed some to her. Lo, and behold she began laying, and getting little feather shafts all over. She looked like a hedgehog chicken, with all the prickles all over. I continued with the show feed, until she was fully feathered, and they were good feathers. Not poor quality, like before. After she finished molting, I put her back on her regular feed. The next year, she lost feathers in sections, not all of them at once. Of course, when she first began to molt, I changed her feed. I can't get the type feed here that you get, so I have to incorporate some animal protein into their diet during molt. It helps a lot.