Matt Mc_Carthy wrote in a message to David Drummond:

 MMC> 15 Dec 2003, 22:26, David Drummond (3:640/305), wrote to Jasen
 MMC> Betts: 

 MMC> Hi David.

 DD>>> How do you achieve the -12V? You'd have to set up your 12 
 DD>>> volters to produce 24V overall, with the centre tap as zero...

 JB>> nah, get ten of them in series and feed 120V DC into the power 
 JB>> socket of the powersupply.

 DD> Does a switchmode supply not need an AC source (as in is it 
 DD> somehow locked to the frequency of the mains)?

 MMC> The very first step inside the PS is to convert the AC input to
 MMC> DC.  No need for _any_ frequency on the mains.

Yep,  no reason you couldn't feed it dc to begin with,  though it'd have to
be at a higher voltage than 120...

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