Symmetric matrix-valued dynamical systems are an important class of systems that can describe important processes such as covariance processes or processes on manifolds and Lie Groups. We address here the case of processes that leave the cone of positive semidefinite matrices invariant, thereby including covariance processes. Both the continuous-time and the discrete-time cases are considered. In the LTV case, the obtained stability conditions are expressed as differential and difference Lyapunov conditions which reduce to spectral conditions on the generators in the LTI case. The case of systems with constant delays is also considered for completeness. The results are then extended and unified into a impulsive formulation for which similar results are obtained. The proposed framework is very general and can recover and/or extend almost all the results on the literature of linear systems related to (mean-square) exponential (uniform) stability. Several examples are discussed to illustrate this claim by deriving stability condition for stochastic systems driven by Brownian motion, Markov jump systems, switched systems, impulsive systems, sampled-data systems, and their combinations using the proposed framework.