Aftermarket External Scanner Pwr Supply

My HP Scanjet 2100C external power supply burned out. HP no longer sells replacements. General store adapters appear to range 300mA and 600mA depending on which one you buy, however the packaging is confusing. I need 120V – 60 Hz – 5 watt input and 9vDC – 100 mA output. Does anyone know if the store adapters will work and/or of any great reference material I can read which deals in greater than A+ detail for power supply specifics on the electronic side? Thanks in advance for any help!