Power consumption is expected to become the main limiting factor for scaling the current network architectures to capabilities of hundreds of terabit or even petabits. The use of optical switching fabrics (SFs) could relax the limitations to some extent but large optical buffers occupy larger area and dissipate more power than electronic ones. In this paper, we evaluate the power consumption of bufferless optical packet switches (OPSs), using the wavelength conversion to solve the output packet contentions. Sophisticated analytical models are introduced to evaluate the power consumption of synchronous and asynchronous OPSs (SOPSs and AOPSs) versus the offered traffic, the main switch parameters, and the used device characteristics. The power consumption in SOPSs and AOPSs is compared when commercial semiconductor optical amplifiers are used to implement SFs and wavelength converters (WCs). The obtained results show that the high power consumption in synchronization stage makes SOPS less effective than AOPS in terms of power consumption. For instance, when the OPSs are dimensioned with a sufficient number of WCs and offered traffic is 0.8, SOPS consumes 140% of power more than does the AOPS. Finally, though power consumption due to cooling system is not considered in the proposed model, we observe that both SOPSs and AOPSs consume much less power per gigabit per second carried than commercial routers.