We verify the existence of Generalized Sudden Future
Singularities (GSFS) in quintessence models with scalar field
potential of the form $V(\phi)\sim \vert \phi\vert^n$ where $0<n<1$
and in the presence of a perfect fluid,
both numerically and analytically, using a proper generalized expansion ansatz for the
scale factor and the scalar field close to the singularity. This
generalized ansatz includes linear and quadratic terms, which
dominate close to the singularity and cannot be ignored when
estimating the Hubble parameter and the scalar field energy
density; as a result, they are important for analysing the
observational signatures of such singularities. We derive analytical
expressions for the power (strength) of the singularity in terms of
the power $n$ of the scalar field potential. We then extend the
analysis to the case of scalar tensor quintessence models with the
same scalar field potential in the presence of a perfect fluid, and
show that a Sudden Future Singularity (SFS) occurs in this case. We derive both analytically and numerically the strength of the singularity in terms of the power $n$ of the scalar field potential.