Here is good brief monograph on carnitine.
Carnitine — Health Professional Fact Sheet

I find the plain l- carnitine less effective (I tried Doctor's Best) not too long ago. Something about the acetyl form seems to work better for me. (however I do notice some acidic vinegary odor sometimes from it on my skin). That is why I went back to the plain L form but I lost stamina on it.

Look up the Juvenon website, as it has lots of information on how carnitine works in the mitochondria especially for aging adults. Dr. Ames did alot of research when offering that product when it was new.