A modern power supply is
essentially a DC-DC converter.
Therefore it first rectifies
the AC power from the wall
into DC.The nice thing about
Such a converter, is that it
can take a whole range of
input voltages and still
Output a constant 12v for our
Pc components.A cheaper power
Supply might use cheaper parts
in the primary side, which is
Why it will only be rated for
200-250v.