Summary : in Public Economics, the simple supply mechanism for a collective good is the centralised provision by government, and paid by all beneficiaries through a small and targeted tax. In the case of capacity adequacy in power supply, which could be considered as a collective good, two solutions of supply by government can be envisaged: a long-term capacity reserve contracting by the system operator (SO), and a direct installation of peaking units by the SO. However, the centralised and direct mechanisms are criticised, because of its potential to distort incentives to invest in peaking units and hence the natural functioning of energy markets. This paper analyses the different characters of a simple capacity mechanism and the safeguards used to limit its potential distortion effects. We discuss its deterrent effects on investment in peaking units. We also demonstrate its advantage in the context of hydro or mixed electricity systems exposed to the risk of exceptionally dry years.