Abstract : We perform systematic calculations of pairing gaps in semi-magic nuclei across the nuclear chart using the Energy Density Functional method and a {\it non-empirical} pairing functional derived, without further approximation, at lowest order in the two-nucleon vacuum interaction, including the Coulomb force. The correlated single-particle motion is accounted for by the SLy4 semi-empirical functional. Rather unexpectedly, both neutron and proton pairing gaps thus generated are systematically close to experimental data. Such a result indicates that missing effects, i.e. including the three-nucleon interaction and the coupling to collective fluctuations, are sub-leading as for generating superfluidity in finite nuclei. We find that including the Coulomb interaction is essential as it reduces proton pairing gaps by up to 40%.