What are adapter?

I am assuming that this question is directly related to the one about the GE rechargeable lighter. The best thing to do is to take this lighter and its charger to a jewelry repair shop. Check around...

Yes, here is an example of what the 300 or 1200mA does for you. The voltage is 9 and that won't change. The mA is the demand you put on that voltage. If you have a spot light that needs 1200mA and...

They are the same thing, just two different ways of saying it. Like kleenex and tissue, same thing.

No, of course not. The 6v adapter only produces 6v, while the load expects 9v.

RS-232 serial ports are far slower than USB ports. With very few exceptions, devices that use USB ports would be impractical to use on a serial port.