  We study the electric and heat current response resulting from an electric
field quench in a holographic model of momentum relaxation at nonzero charge
density. After turning the electric field off, currents return to equilibrium
as governed by the vector quasi-normal modes of the dual black brane, whose
spectrum depends qualitatively on a parameter controlling the strength of
inhomogeneity. We explore the dynamical phase diagram as a function of this
parameter, showing that signatures of incoherent transport become identifiable
as an oscillatory ringdown of the heat current. We also study nonlinear
conductivity by holding the electric field constant. For small electric fields
a balance is reached between the driving electric field and the momentum sink
-- a steady state described by DC linear response. For large electric fields
Joule heating becomes important and the black branes exhibit significant time
dependence. In a regime where the rate of temperature increase is small, the
nonlinear electrical conductivity is well approximated by the DC linear
response calculation at an appropriate effective temperature.
