Can a hydrogen generator subsidize my Jeep's gas?

No your engine is working harder to make the HHO Gas. Your alternator isn't making any extra electricity, it makes enough to charge the battery, run the lights, radio, etc. As you use them you burn slight more fuel, to make more electricity, turn them off you make less.

But here's an easy way to show it's a scam (which has been around since the 1970's and yes I'm that old)

They say your going to get 10 to 200% better fuel mileage, (depending on what site you got too). Let us the 10% number. Now to get 10% better fuel economy you MUST increase the efficiency of the engine by at least 10%. So let say your engine make a 145 to 265 HP depending on the year. That that would mean your engine would make 14.5 to 26.5 extra HP. and that would be easy to measure. The problem is that you NEVER see the increase in HP when the devices are tested. Oh before I forget odds are it's a crime is mess with the emissions system on you Jeep, (they generally say it'll lower your emission, it won't, but unless it's been tested and approved you might find yourself looking at a huge fine.)

It's a scam, but I will help you save fuel.

1. get rid of any excess weight, clean your jeep out of any junk you're just carrying around

2. Make sure your tires are properly inflated, check them WEEKLY.

3 don't drive over 60 MPH

There I just saved you more fuel with any one of those then you will ever save with the silly HHO device.

No. It cannot.

The drag on the engine caused by the generator will be greater than the energy produced by the generator.

The guy you're gonna buy it from is either ignorant or trying to rip you off.

No. It's a scam. Your engine has to work harder to provide the energy to make the HHO