An analytical expression for the jet power extracted from the disc (JPEFD) is derived based on an equivalent circuit in black hole magnetosphere with a mapping relation between the radial coordinate of the disc and that of unknown astrophysical load. It turns out that this JPEFD is comparable with two other JPEFDs derived in the Poynting flux and hydrodynamic regimes, respectively. In addition, the relative importance of this JPEFD relative to the Blandford–Znajek power is discussed. It is shown that the BZ power is generally dominated by the JPEFD except in some extreme cases. Furthermore, we show that the JPEFD derived in our model can be well fitted with the jet power of 3C 273.