Yes you can. Given the fact you're talking about milliamps - the slight increase in amps will have no detrimental effect.
yes this will work fine
You can use any 9v adapter as long as the output amperage is rated higher than the amperage rating of your appliance so yes a 600ma adapter can be used to power a 500ma or 400ma appliance
no .never
Yes, no problem whatsoever as long as the voltages are the same. The adapter's capacity is 1000 mA and your device only requires 500 mA. The draw from the adapter is only at 50%.
Your question is confusing, but if you are asking whether you can use a 9V/250 mA adapter to supply a load device rated at 5 V/1000 mA, then the rule is quite straightforward. The adapter's rated output voltage must match that of the intended load, but its rated current must exceed that of the load. So in your example, you cannot use the adapter with the intended load.
I think you mean to ask if one can use a 9v 600mA adapter to power a 9v 300mA appliance. Yes, you can do that. A 9v 600mA adapter will deliver 9v at up to 600mA. A mA is one milli amp, or one thousandth of an amp. 300mA is 300 thousandth of an amp, 300/1000 or 0.3 amps. 600mA is 600 thousandth of an amp, 600/1000 or 0.6 amps, and is twice the current of 300mA.
No you can not. The power supply output of 5 volts is under sized. There is no way that a 45 volt device would operate from it. You will need to find a power supply of 45 volts.
12v 1000mA means that the maximum output of that unit is 1000 milliamps at 12 volts. 12v 150 mA means that the maximum output of that unit is 150 milliamps at 12 volts. So if you need 150 milliamps at 12v either will do. BUT if you need over 150 milliamps at 12v then you must go for the 1000 mA unit. By the way there are 1000 milliamps in 1 amp.
Using a 12v 600ma source is allowing 12 volts and 600 amps of power. If the device requires a 12v 500ma source, the larger source is acceptable. Please note that it will only be drawing on 500ma of the available 600ma.
input voltage is strictly according to applications. If use 12V dc adapter power 5V dc device, the 5v dc device would be damaged.
Possibly, but not if you want to invalidate the warranty to your appliance.
no, different voltage could fry solid state components.