Solutions of the wave equation are analyzed considering the propagation of electromagnetic fields through a non-homogeneous stratified metamaterial medium. These solutions are obtained by two methods: (1) Spectral Parameter Power Series (SPPS) and (2) SPPS with Operator Transmutation (OT). This last method is considered an innovation for this application. Numerical solutions are obtained for left-handed (LH) and right-handed (RH) media, which allow their reflectance and transmittance coefficients to be calculated. The performance of each method is evaluated by comparing their solutions with the exact ones available and with those obtained by the differential transfer matrix method (DTMM). The advantages and limitations of each method are indicated.