Whether the voltage doubler will deliver such currents like 1Amp at 24V?
As rightly pointed out by Audioguru, we may have to look for better converters.There from Viper50 etc, from ST Micro, and LNK switch from Power Integration Inc for converting 12 to 24.
24 to 20 conversion for 1 amp load, LM317 will suite, but needs a good heat-sink.
If it is for end use and one off, (not a project work) It is also possible that Rahuljin can use Pinter power adapters, as they are available for a throw away price and are available at 20V and 19V also.