A: No problem but don't expect the power to increase
A: Disregarding the fact of different voltages there is the power to be concerned 9v x 1A = 9W, 15V X .8 = 12W. THE DEVICE WILL BE UNDER POWER.
You would need a 9V dc supply. The potential current output of you supply myst be greater than or equal to the current draw of the pedal. (100ma load on a 150ma supply: fine. 150ma load on a 100ma supply: bad.) With these conditions met you can just get another 9V snap and wire it to your supply. Remember, as you are connecting two snaps together, the polarity of the snap for your supply will be reversed. (Red is - and black is +) CHECK YOUR WORK! If you mix up the polarity, you could smoke your pedal. You can also make your own regulator with a LM317 voltage regulator from a higher supply. This will only work with another low voltage DC supply with a voltage output higher than 9V. It will not boost the voltage and will not work with line voltages. It is a common IC and many manufacturers make them. Check your pedal. Most of them have DC in jacks so you don't need to hook to the battery clip.
The device that changes d.c. into a.c. is called an 'inverter'. Whether you can get one for 9 V is another question!
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.
No, of course not. The 6v adapter only produces 6v, while the load expects 9v.
6V dc motor
Yes, the manufacturer specifies what the working voltage of a device will be and that voltage has to be adhered to.
A: No problem but don't expect the power to increase
using dc-dc converter
No you should not do that. It will damage the battery and the battery will explode.
Yes you can. Given the fact you're talking about milliamps - the slight increase in amps will have no detrimental effect.
A device which requires 1000mA at 9 volts in order to operate will not work from an output of 500mA. This output is only half the power requirement of the device.
conclusion of dc power supply 9V
No. 9 v is only 75% of 12 v.
No. Usually it's a -/+ 10% difference. So, a 9v would need at least 7.2 volts or more
No, it is not recommended to plug a 9V DC power source directly into a 220V outlet. Doing so can damage the device connected to the 9V source and pose a safety hazard. It is important to match the voltage requirements of the device with the power source to avoid potential damage or injury.