  In this work we show that the general singlet extension of the MSSM can
naturally provide a self-interacting singlino dark matter to solve the small
cosmological scale anomalies (a large Sommerfeld enhancement factor can also be
obtained). However, we find that the NMSSM (the singlet extension of the MSSM
with Z3 symmetry) cannot achieve this due to the restricted parameter space. In
our analysis we introduce the concept of symmetric and antisymmetric viscosity
cross sections to deal with the non-relativistic Majorana-fermion dark matter
scattering.
