No. 9 v is only 75% of 12 v.
if you have 12v dc then you can use a 4 ohm resistor
no, different voltage could fry solid state components.
No, not possible. The charger has to go to higher volts than the battery being charged.
In Digital multimeter we use 9V Dc battery.
using dc-dc converter
No.
That's almost twice the voltage. The chances of frying your device is high.
No, you cannot.
DC 12V power supply can convert 110/220V AC power source to 12V DC.
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.
Not a good idea. It will raise the current that could burn out components. To repair you would need to determine what was burned out and how easy it would be to replace.
Battery chargers have a 12v DC output.