None proven to help. Men who are worried about their sperm and semen are usually trying to have a baby, so may end up buying and taking supplements advertised to help sperm, just for the extra ounce of hope. The uncertain amounts of l-carnitine, vit. E, folic acid, vit. C, or coenzyme q10 that may be in the supplements, along with uncertain amounts of "other" ingredients, have not been proven to help sperm or semen.
YES proven to help! At least 3 herbs have been proven in published studies to improve sperm count and motility: maca, tongkat ali & mucuna pruriens. There is also evidence that ginseng, ashwagandha and tribulus may be helpful. Reliable standardized extracts are available. Other nutrients like zinc & l-carntine/acetly-l-carnitine can help too. See http://www.Raysahelian.Com/fertility.Html for a summary of research.