There is no simple answer. If the compounds you are analyzing are not in a mass spectral database, you can use exact mass and isotope information to obtain candidate elemental compositions. In my Mass Mountaineer software, I first obtain an elemental composition and then search local or on-line databases for candidate compounds with the given composition.
If you are searching MS/MS spectra, the NIST mass spectral database includes MS/MS databases with spectra from different mass analyzers. The low-energy CID mass spectra will be very similar for QTOF’s, in-source CID, and triple quadrupole mass spectrometers. Of course, fragmentation will vary with collision energy, so there are multiple spectra in the database for different collision energies. You can also search drug spectra against the NIST DART Forensic database.