A comparison of the best-fit results derived from single-round, multiple-round inference and XSPEC. Left: posterior distribution comparison between XSPEC spectral fitting and SBI-NPE, as applied to the persistent emission spectrum of 4U1820-303 (pre-burst). The spectrum is modeled as tbabs*(blackbody+powerlaw). There is a perfect match between the three methods, not only on the best fit parameters, but also on the width of the posterior distributions. Right: count spectrum of the persistent emission, together with the folded model derived from both SBI-NPE and XSPEC. The C-STAR of the best fit is indicated together with its deviation against the expected value.