On 2012-01-19 12:31:10 +0100, "William Sommerwerck"
said:

Buy an inverter that converts 12V DC to 120V AC. Then use an
AC power supply ("wall wart") suitable for the boombox. It might
even have its own built-in AC adapter.

total waste of energy ...

WHY?

It requires no energy -- it's plug 'n play.

I'm not talking of human energy, but electricity energy ...
each time you convert voltage (12v-120V) then 120V-9V
you have power losses, that generate heat.
that means the energy if transformed into heat, useless and poor solution
for the planet ...
instead use a smps converter from 12vdc to 9vdc they exists
they are cheap, and the power losses are reducted to a minimum

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