No, the unit might work but the low voltage will cause unit to stop.
No, the voltage from the adapter should match the voltage required by the appliance.
It sounds like the same thing to me.
No, of course not. The 6v adapter only produces 6v, while the load expects 9v.
No, if you use a 6 volts adapter instead of a 9 volts adapter, you will be supplying 3 volts too little to the item that requires 9 volts. Either it may not work properly or it won't work at all. The fact that the 6 volt adapter can supply more current (2000 mA instead of only 1200 mA) won't help solve the problem of having insufficient voltage.
Using a 6 volt adapter on a 9 volt phone can potentially damage the phone. The lower voltage may not provide enough power for the phone to function properly, leading to issues like slow charging or irreversible damage to the phone's components. It is always recommended to use the voltage specified by the manufacturer to avoid any damage.
No, it will overcharge the 6 volt battery.
No. The voltage difference is too great. There are types of adapters in the market place that have variable set point voltages. You can usually go from 1.5,3,4.5,6,7.5,9 and 12 volts with these types of wall plug in adapters.These types of adapters also come with different end type connectors for connecting to many different devices.
If you are talking about a 6 volt coil, yes, so long as the contacts are rated for the 230 volt circuit. If you are talking about 6 volt contacts, no, absolutely not.
USE INVERTER USE INVERTER USE INVERTER
Car Bomb
It might work if the device that you are plugging it into has its own voltage regulator, there is no way of knowing this. Personally I would not take the chance. When a manufacturer designs a piece of equipment it uses a specific voltage for the circuitry to operate on. Varying from this voltage is not a good idea and most likely it will void the warranty if the device becomes inoperable.
A D-cell delivers around 1.5 Volt per piece. NORMALLY (but not always!) six D-cell are joined in series to make 6 x 1.5 = 9 Volts. Only in cases where a high current is needed there may be a facility to have 2x 3 serie cells in two branches parallel thus making it 4.5 Volts. It is quite safe to assume you will need a 9 Volt AC-powered adapter for this equipment, exceptions observed. With kind regards, Henk