carnitine has a definite effect on increasing ketosis and thus also in general energy utilization. i don't know the details of the suspected mechanisms but i know that's a major selling point for it, you can find carnitine and NAC in most body building supplement suppliers catalogs.
the N-acetyl ester is just more bioavailable form of carnitine, for similar reasons that diacetyl morphine is more bioavailable than morphine (the brand name "heroin" is literally the same modification of morphine as NAC is to carnitine). of course, backyard chemists can't get access to the easy reagent for doing this, there is other ways involving halo-substituted acetyls and such.
