Between the RTI Act and OSA, RTI Act has its primacy.
Section 22 of the RTI Act provides for its primacy vis-a-vis provisions of other laws, including OSA.
This gives the RTI Act an overriding effect, notwithstanding anything inconsistent with the provisions of OSA.
So if there is any inconsistency in OSA with regard to furnishing of information, it will be superseded by the RTI Act.
However, under Sections 8 and 9 of the RTI Act, the government can refuse information. Effectively, if government classifies a document as “secret” under OSA Clause 6, that document can be kept outside the ambit of the RTI Act, and the government can invoke Sections 8 or 9. (Legal experts see this as a loophole)