In South Africa, one of the instant release Ritalin generics is called METHYLPHENIDATE HCL-DOUGLAS (catchy, right?)
When I used to snort the substance, Ritalin didn’t feel as potent as the generic. Was a bit annoying to crush too. Orally, I couldn’t really tell the difference.
I had a little milligram scale. I don’t recall the exact mass, but I remember the Ritalin tablet being considerably heavier than the generic.
Could be the different types of binding agents, preservatives or whatever else a pill needs to be a pill besides the active pharmaceutical ingredient not working well in your system.
Otherwise, try to take it easy. As far as I recall, stims and bipolar disorder don’t play nice long term. One of my closest friends who had the disorder sadly never managed to kick his coke habit.