  We consider non-stationary spherically symmetric $n$-dimensional charged
black holes with varying mass $m(v)$ and/or electric charge $q(v)$, described
by generic charged Vaidya metrics with cosmological constant $\Lambda$ in
double null coordinates, and perform a comprehensive numerical analysis of the
fundamental quasinormal modes (QNM) for minimally coupled scalar fields. We
show that the "instantaneous" quasinormal frequencies exhibit the same sort of
non-stationary behavior reported previously for the four-dimensional uncharged
case with $\Lambda=0$. Such property seems to be very robust, independent of
the spacetime dimension and of the metric parameters, provided they be
consistent with the existence of an event horizon. The study of time dependent
Reissner-Nordstr\"om black holes allows us to go a step further and quantify
the deviation of the stationary regime for QNM with respect to charge
variations as well. We also look for signatures in the quasinormal frequencies
from the creation of a Reissner-Nordstr\"om naked spacetime singularity. Even
though one should expect the breakdown of our approach in the presence of naked
singularities, we show that it is possible, in principle, to obtain some
information about the naked singularity from the QNM frequencies, in agreement
with the previous results of Ishibashi and Hosoya showing that it would be
indeed possible to have regular scattering from naked singularities.

General Relativity and Quantum Cosmology