Power consumption of a ATP synthase in Watts
There are tons of mechanistic studies of ATP synthase so you may be able to get a better answer from finding one of those. But here's a rough estimate based on thermodynamics and enzyme kinetics.

The $\Delta G$ of ATP synthesis/hydrolysis is about -50 kJ/mol. The $V_{max}$ is in the low hundreds (here is an estimate of 350 $s^{-1}$ for E. coli ATP synthase), giving you something like 17 MW/mol or 30 aW (3e-17 W) /molecule.

I did look briefly at some mechanistic studies, and found this reference of 80 pN * nM for the torque generated. That translates to almost exactly the same 50 kJ/mol (ATP synthase is very efficient). But of course you still need the $V_{max}$ (number of rotations per second) to get the power.