Just repaired a blown fogger unit, reversed battery.
Used a Component Shop LM2557 switch mode converter unit running from 12v (max) and giving 1 amp at 24v, plenty for the fogger that requires 300Ma. I may add a small heatsink if the chip gets hot as the fogger has no off switch whilst on the water.
There is a simple multiturn pot adjustment to set the required voltage.
Fogger now working full pelt and as good as new.