  We report on the 2020 reactivation of the energetic high-magnetic field
pulsar PSR J1846-0258 and its pulsar wind nebula (PWN) after 14 years of
quiescence with new Chandra and Green Bank Telescope observations. The emission
of short-duration bursts from J1846-0258 was accompanied by an enhancement of
X-ray persistent flux and significant spectral softening, similar to those
observed during its first bursting episode in 2006. The 2020 pulsar spectrum is
described by a powerlaw model with a photon index Gamma=1.7\pm0.3 in comparison
to a Gamma=1.2\pm0.1 before outburst and shows evidence of an emerging thermal
component with blackbody temperature kT=0.7\pm0.1 keV. The 0.5--10 keV
unabsorbed flux increased from 5.4e-12 erg/cm^2/s in quiescence to 1.3e-11
erg/cm^2/s following the outburst. We did not detect any radio emission from
the pulsar at 2 GHz and place an upper limit of 7.1 uJy and 55 mJy for the
coherent pulsed emission and single-pulses, respectively. The 2020 PWN
spectrum, characterized by a photon index of 1.92\pm0.04 and X-ray luminosity
of 1.2e-35 erg/s at a distance of 5.8~kpc, is consistent with those observed
before the outburst. An analysis of regions closer to the pulsar shows
small-scale time variabilities and brightness changes over the 20-yr period
from 2000 to 2020, while the photon indices did not change. We conclude that
the outburst in PSR J1846-0258 is a combination of crustal and magnetospheric
effects, with no significant burst-induced variability in its PWN based on the
current observations.
