Can I use 1500mA adapter on a 500mA device?

You don't want to get the voltage off too far. It may or may not be ok to use 10 volts instead of 9, it depends on how sensitive the device is to this. The current rating on the supply is its maximum capability, it doesn't force this amount on the device. If the device requires 500 mA from the 9 volt supply the 1000 mA supply will power it just fine. The impedance of the device when in operation is apparently about 18 ohms. You put 9 volts across 18 ohms with a minimum of 500 mA available and the device will draw 500 mA from the supply. You put 9 volts on it using a super supply with infinite current capability and the device will still draw 500 mA and work fine.

mk