What is the actual voltage from the DC power supply across the + and -
battery terminals when you attempt to use the supply and have the toy
activated? My guess is that the batteries are putting out more current than
the supply is capable of delivering or the gauge of wire you are using is
too small. In either case the voltage at the battery terminals should be
well under the 4.5V nominal and is likely insufficient for the application.
The solution here is a larger capacity supply and/or heavier gauge wire.

Another possibility is that the DC supply you are using may have high AC
ripple thereby reducing the effective voltage. In this case you can add a
large filter capacitor and see if this improves the performance.

Bob

wrote in message
oups.com...
I've got a piece of electronics on my bench that is normally powered by
3 C batteries, wired in series and thus producing about 4.5 Volts. I
wanted to power this device with a bench power supply just so I don't
drain the batteries while I'm experimenting with it for hours.