No. You will need a transformer to step up the voltage and you will possibly need to convert the plug.
No you shouldn't use a 14 volt 5 amp adapter on a 12 volt 5 amp device unless you know for sure that the 12 volt device has an internal voltage regulator that will lower the voltage to the correct voltage range the device was designed to use. As long as you always take care to check the output voltage with a voltmeter first, to be sure that the voltage from the adapter is regulated, meaning that it does not rise when a lower current in amps is drawn from it, you may be able to use an adapter that gives the right voltage at a higher amp output rating than the device actually takes. (For example, it may be possible to use a 12 volt 7 amp adapter for a 12 volt 5 amp device.)
A transformer can step up or step down AC voltage
Yes, a 110 volt device can be plugged into a 125 volt receptacle. The voltage rating on the receptacle is only there as the highest voltage supply that the manufacturer recommends their equipment be connected to.
No, the voltage difference is too high.
It's an ac voltage-converting device with an output voltage of 220 v.
The unit of voltage is the "volt". The unit of current, sometimes called "amperage", is the "ampere".
No, a 240 volt device runs on 240, and a 120 volt device runs on 120. Attempting to run a device on incompatible voltage results in damage.
No you shouldn't. Doubling the voltage will double the current through the device. This in your case will apply 24volt to the device connected to the downconverter and will burn it out.
Power equals the product of current and voltage. The power used by a 9 amp 27 volt circuit is 243 watts. The power produced by the device, however, depends on the device's efficiency.
A device that melts under high current , not high voltage is a circuit protective fuse. There are many fuses that are rated for voltages in the 10,000 volt range. It is the over current that trips them.
There will be no effect on the voltage. That is the effective voltage will be only 12 volt. But there will be increase of current.
No. A volt-ohmmeter will not check insulation. To check cable insulation you need a special device (called a megger) made for the purpose that imposes a high voltage and measures current leaks.