There lacks a generic representation of the wave power absorption of devices across dimensions, shapes, and resource conditions. A conventional resource assessment approach only evaluates the wave power based on wave characteristics, which is insufficient to capture the practical power absorption variations between WEC archetypes. In this paper, a novel WEC net power assessment (WNPA) method is proposed and is generally applicable to any arbitrary WECs design. Two theoretical upper bounds of wave power absorption are adopted and derived for different types of WECs. Numerical simulations are conducted to apply this novel technique to assess the net power available to different WECs at the Wave Energy Test Site (WETS), Hawaii and the PacWave site, Oregon over 11 years. By comparing the power potential for WECs oscillating in different degrees of freedom, the results indicate the surging mode may be the most energetic; regardless of shapes and ocean sites. When applied to three generic WECs (point absorber, terminator, and attenuator), the pitching terminator is shown to have lower absorption potential. Finally, the mean annual energy production (MAEP) of the three generic WECs at WETS and PacWave are compared, and a surging attenuator shows a significant wave power potential at PacWave.