Here is a more basic type:
How to measure current and power - using a hall effect transducer - clamp
It's gonna take some homework
If you are thinking a plugin solution then perhaps a separate voltage reg. So roughly speaking we are trying to turn anything above, say .5 amps into >2.5 volts. With maybe 5 amps current capability. Might be a hall effect and a mosfet. Dang, clamp on would be nice
worth doing some homework for that.