The next generation mass probes will investigate DE nature by measuring non–linear power spectra at various z, and comparing them with high precision simulations. Producing a complete set of them, taking into account baryon physics and for any DE state equation w(z), would really be numerically expensive. This seminar introduces to essential regularities reducing such duty, in particular a suitable spectral equivalence implemented in the PKequal package, and included in the official version of CAMB.