I was under the impression (false one appraently (I read Lubos Motl answer in stackexchange)) that Schwinger's theory which is covered in his three volumes called "Particles, Sources and Fields.", is really only a different interprataion to QFT, but the end results are the same. Now I read the special preface of volume three and it's written that:" ...Particular attention should be directed to Section 5-9, where, in a context somewhat larger than electrodynamics, a disagreement between source theory and operator field theory finally does appear." So does Schwinger's theory genuine different than QFT? Unfortunately I don't have time now to read thoroughly his three volumes, maybe after I am done with my PhDs.