[Question]: I have a 3A power supply, will it break my 500mA circuit?
No. A 3A power supply will not force 3A into your circuit. A 3A power supply will supply up to 3A of current. It’s your circuit that decides how much of that current it will actually use.
[Question]: My device says 5V (DC) 1A. What power supply do I need?
You need a power supply that gives 5V DC and has a maximum current of 1A or more.
[Question]: My circuit needs 9V, can I use my 12V supply?
No. If your circuit needs 9V and you connect it to 12V, it’s a good chance it will break.
Learn the basics of choosing a power supply here:
Keep On Soldering!