Best Circuit Design for a 12VDC Wall-Wart > Ouput Voltage of 1.5V (Replacing Alkaline Batteries)
I'm surprised the rocker doesn't have a DC inlet already.

You could connect the 9 V supply to a linear 1.5 V regulator, and it would be easy, but you'd be wasting a lot of energy.  It would be better to just go to a thrift store and try to find wall warts that are close (more appropriate transformer turns ratio) to the voltage you need.  Regulating a 3.3 V or 5 V supply down to 1.5 V would be more efficient.  The voltage might not even need regulating, or could be anywhere within a large range and still work, but you'd have to take the products apart and see what they feed into.  I ruined a digital camera by accidentally using a higher voltage adapter, but many things don't care.