What is the difference between adderall (dextroamphetamine and racemic amphetamine) xr 20mg and adderall (dextroamphetamine and racemic amphetamine) d-amphetamine salt combo 20mg?

Unclear question: Adderall (dextroamphetamine and racemic amphetamine) is a mix of two salts of amphetamine (amp) with half being d-amp and the other half being d/l-amp. Only d- amp is active for adhd sx. I suspect the latter you mentioned is immediate release, as opposed to extended release (xr). The medication is the same, but the former lasts about half as long as the latter. So, 20 mg XR is like taking 10 mg in the morning and another 10 mg at noon.

Brand Name VS GENERI: Adderall (dextroamphetamine and racemic amphetamine) XR is the brand name of an extended released tablet intended to give a double pulse delivery of amphetamine compared to conventional adderal immediate release. The adderal XR contains sulfate salts of dextroamphetamine, dextro isomer of amphetamine saccharate and dexroamphetamine aspartate monohydrate. The combo salt is the generic type.