Yes, you can use a 300mA adapter on a 1A device, but it may not work properly or could damage the adapter. The device may draw more current than the adapter can provide, leading to insufficient power, potential overheating, or failure of the adapter. It's always best to use an adapter that meets or exceeds the device's current requirements for optimal performance and safety.
Using a 9V 600mA power supply to replace a 9V 1A power supply may not provide enough current to power the device properly. It is important to match the voltage and exceed the current requirements of the device to avoid damage or malfunction.
No, neither will work and they may even be damaged.
12 + 1a - 1a + 1 = 1 + 0 + 1 = 2
No. If it works at all, it will be underpowered, and possibly damage the speakers. To power 12V speakers, you have to have an adapter with EXACTLY 12V (no more, no less), and at least 1A. You could hook up a 12V 4A adapter if you wanted to, your speakers would just only draw 1A of power. Make sure you use a 12V adapter though!!
Output: 5V 1A
Yes.
Unfortunately no, if the device calls for 2000ma you will need a 2A (amp) power supply to adequately power it.
1a.
(x + 4) + (x + 5) = 2x + 9
No, the new adapter will not be able to safely supply enough current.
1a + 1b because they are different terms and could not be added together. But 1a × 1b would be 1