This work proposes a novel adaptive bistable power capture mechanism, which is applied to a point absorber wave energy converter in regular waves. The adaptive bistable mechanism is realized by two symmetrically oblique main springs (responsible for the bistable characteristics) together with two auxiliary springs (making the bistable system adaptive) and it can adjust the potential function automatically to lower the potential barrier near the unstable equilibrium position. The "adaptive" feature helps solve the low-energy-absorption problem of a conventional bistable wave energy device (whose potential function is invariable in time) caused by the intrawell oscillation in low-amplitude excitation. With a suitable choice of physical and geometric parameters, an adaptive bistable wave energy converter outperforms its linear counterpart while a conventional bistable wave energy device has a poorer performance in low amplitude waves. Even for relatively large waves, an adaptive bistable wave energy converter has a comparable power capture capacity with its conventional bistable counterpart, both of which perform better than a linear wave energy converter especially in the low wave frequency region.