  One of the hallmarks of the Berezinskii-Kosterlitz-Thouless (BKT) transition
in two-dimensional (2D) superconductors is the universal jump of the superfluid
density, that can be indirectly probed via the non-linear exponent of the
current-voltage $IV$ characteristics. Here, we compare the experimental
measurements of $IV$ characteristics in two cases, namely NbN thin films and
SrTiO$_3$-based interfaces. While the former display a paradigmatic example of
BKT-like non-linear effects, the latter do not seem to justify a BKT analysis.
Rather, the observed $IV$ characteristics can be well reproduced theoretically
by modelling the effect of mesoscopic inhomogeneity of the superconducting
state. Our results offer an alternative perspective on the spontaneous
fragmentation of the superconducting background in confined 2D systems.
