Not familiar with your particular make/type of scanner, but I'd expect the scan lamp to illuminate once it had power applied and was switched on.
If your scanner has the facility, make sure the carriage is unlocked before your try powering it up.
If the scanner requires 12vdc, then feeding it with 9vdc may preclude it from working. Often the voltage and current requirements are printed on the back or bottom of the scanner. Failing that, go check with the operating manual, or download a PDF from the manufacturer's website.
It sounds like you are possibly not using the correct, or original PSU. Apart from undervoltage, failure of the PSU to supply sufficient current (Amps) may also prevent the scanner from working.
ROGER - G0AOZ.