the civilpedia says that if you add the great general to your city you should then get +2 experience per military unit created. i added two separate generals to two different cities (one a capital, one not), and I got no more experience per unit than granted by the barracks. The units get produced with only 3 experience (because there is a barracks in both cities, already) as was done before adding the great general.
I am using BTS v3.13.
I am using BTS v3.13.