I have been diagnosed with idiopathic hypersomnia. Adderal is not consistently effective. Why? Is there something else more effective?

Right for you. The most effectiveedicstion is the one that works for you. Every human is truly an individual. Talk with your doctor about how the Adderall (dextroamphetamine and racemic amphetamine) is working for you. We are here to help you.
Hypersomnia drugs. Two drugs on the market, Nuvigil and Provigil have been tested for this condition.
Sleep disorder. Did you actually have a sleep study to make the idiopathic diagnosis or was this just by history? Idiopathic, i was taught meant that the patient is pathic and the doc an idiot. I would recommend a further work-up including a new sleep study, assessment for anxiety, depression and medical causes of hypersomnia eg, anemia, auto-immune, internet addiction....
Tolerance develops. Tolerance takes away much of the wakefulness produced by stimulants like adderall-- i.e. Amphetamine. Other meds used are Provigil or nuvigil; they are used with stimulants, or alone. They have some tolerance as well, that takes away a portion, not all, of their effect. Finally, xyrem, for, narcolepsy; improves deep sleep, reducing daytime sleepiness- in case you were misdiagnosed.