  We propose a model for the origin of the broad He II 4686A emission in the
early spectrum of type II SN~2020jfo. The 4686A line is emitted presumably by
dense fragments embedded into a hot gas of the forward shock wave. The
fragments are produced as a result of a heavy braking of the dense low-mass
shell at the ejecta boundary and a simultaneous Rayleigh-Taylor instability.
The temperature of line-emitting fragments is $\approx$5$\times10^4$K.
Calculations of ionization and excitation of helium and hydrogen account for
the He II 4686A luminosity, the large flux ratio of He II 4686A/H$\alpha$, and
a significant optical depth of the 4686A line. We demonstrate that fragments
heating by hot electrons behind the forward shock compensates cooling via the
HeII 304A emission.
