Flip all the breakers in your converter one at a time. Just start from the top and go right down. If, after flipping them all, nothing changes, check your outlets for a GFI outlet and push the button there. If that doesn't help, then there's other issues going on.
Sometimes it really is hard to see which breaker is actually flipped. But more than likely, this is all that happened. Next time, you'll know which breaker it is, and you also know not to run both appliances at the same time.
We all learn this, and learn to manage our power, because there really is only so much you can run on one circuit before the breaker pops.
Good luck!
Edit:
Just re-read your original post. In my current camper we can run 1 electric ceramic space heater, but not 2 at the same time, even on different circuits.
We can run the microwave and air conditioner at the same time, but if we plug in an electric skillet or our electric griddle, or a toaster, (with) the water heater running, the main breaker blows.
We have since decided to use the water heater on gas all the time. This prevents the main breakers from blowing, especially when adding a toaster or something else.
What we started doing was to plug in another electric cord (we have a 100 foot cord) and plug it into the shore power outlet for a regular household plug (15-20 amp plug). We run the other end of the extension cord into the camper and plug in our extra appliances there. We use that extension cord for the toaster, or the electric griddle, or the 2nd ceramic space heater.
When camping and we are outside, the same wire is used to power the electric griddle, electric skillet, or toaster outside on the picnic table. If we bring the television outside, we use this same cord to power it outside too. All this to prevent plugging directly into the camper and running power through it's system to prevent breakers from popping.
This works.
