EDM power supply

Hi!

In many sites over the web I can read about beautiful properties of
anti-electrolysis EDM.
But nowhere I can read what exactly is special with those anti-electrolysis
power supplies. Seems there must be some AC, or pulses instead of just DC.
Anybody can comment anything on this topic? Maybe any sites with useful info?
I would like to design such a power source as a University project but do not
know any specifications needed.

TIA,

KPL