I see that lots of people add ephedrine to their ephedra-free thermogenics [which usually contain synephrine], and I wonder if ephedrine is simply superior to synephrine in every aspect and they do this simply to counter the removal of ephedra, or if they actually work synergistically together.
Most likely ephedrine is added to counter the removal of ephedra. If ephedrine (or even ephedra) and synephrine worked synergistically together then you probably would have seen them together in pre-ban formulations.
Synephrine is an alpha(1) agonist, whereas ephedrine is mainly a beta(2) agonist. The ability of synephrine to aid in fat burning is minimal, to my knowledge; its role is mainly as an appetite suppressor. Ephedrine + Caffeine suppresses appetite pretty well as it is, but adding 10mg of Synephrine with each E/C dosing enhances the anorectic effect nicely.
Synephrine would really shine more in something like a clen cycle, where the appetite is stimulated rather than suppressed by the lipolytic agent. Nicotine would do a better job in this respect, but Synephrine is dirt cheap, so it makes a nice addition to just about any cutting stack.