More current parraraling up...

Using 2 or 3 7805’s or 2 or 3 transistors, due to voltage missmatch and one burning out due to excessive current from a higher voltage…

So how do inverters get around this problem?

Simple question, but there is no simple answer.

7805 : you can not use them parallel.

Transistors for voltage output can be placed parallel, each with a base resistor to reduce the differences.
If have made a power supply with three output transistors. I have matched the base resistor to the transistors to make them as equal as possible. Maybe a transistor heats up more than an other, I don't know. They are all on the same heat sink.

Inverters that use switching mosfets is a lot easier, since there is no analog regulator involved. A mosfet that is 'on' is a few milli-ohms. Those can used parallel without any problem.

cjdelphi:
Using 2 or 3 7805's or 2 or 3 transistors, due to voltage missmatch and one burning out due to excessive current from a higher voltage...

So how do inverters get around this problem?

3 7805's - doesn't work because they have internal feedback.

3 transistors - sure, why not (so long as they're all saturated...)