The Aquadopp, AquaPro, AWAC, Vectrino and Vector can adjust its power over four levels in roughly 6 dB steps.
A difference of 6 dB is about a factor of 4 in power. At the lowest level, the instrument uses little energy for transmit, while at the highest level, most of the energy consumed by the instrument goes to the transmit pulse. Higher transmit power allows the instrument to work in lower backscatter, but it causes the battery to deplete faster.
In principal there are only two power levels. Both High levels runs directly from the power supply voltage, while the Low levels runs from a DCDC converted 3.3V supply.