  Black holes typically inhabit highly dynamical galactic environments and are
frequently permeated by accretion media. The inevitable scattering of scalar,
electromagnetic and gravitational waves off rotating and charged black holes
provides a remarkable demonstration of the energy extraction and subsequent
amplification of scattered waves under the expense of the compact object's
rotational and electromagnetic energy; a phenomenon known as superradiance.
Certain circumstances tremendously favor the energy extraction process in such
extent that linear superradiant instabilities are triggered. We examine the
superradiant amplification of monochromatic charged scalar fields impinging
Reissner-Nordstr\"om-de Sitter black holes which are known to exhibit
superradiantly unstable quasinormal modes. We find that even though the
frequency range of superradiance is reduced when a positive cosmological
constant is incorporated, the amplification factors are significantly elevated
with respect to those occurring in Reissner-Nordstr\"om spacetime.
Intriguingly, we confirm that the long-lived quasinormal resonances that reside
in the superradiant regime induce resonant peaks when the wave's frequency
matches the real part of the quasinormal mode, regardless of the spacetime's
modal stability.
