On Sun, 19 Jul 2009 14:19:10 -0400, Michael Robinson wrote:

The main heater (the one that fuses the toner so it sticks to the
paper) is usually run on a thermostat, using a big SCR (triac, to
be more specific). Those SCRs can trigger on fast-rising spikes
on the power line, by capacitive coupling from cathode to gate,
so steps in the power-in voltage are contraindicated.

So a heater of that sort takes its power directly from the line?

There's no reason to use DC, particularly if it means that you need a
1kW PSU instead of 200W.