DSA doesn't give you more money, unless it's to refund cash spent on pre-approved expenses.
DSA is intended to provide extra help, equipment and facilities which counteract any practical problems you may have with studying or uni life, caused by medical conditions.
Part of your application is a formal face-to-face assessment. Anything awarded under DSA is based on the impact your condition(s) has on you. If you have a medical condition which doesn't cause a problem with studying or uni life, then you won't get DSA.