PC PSU - 24V, 36V, 48V .. etc.. from a 12V PC power supply?

Hmmm..

Has anyone here tried connecting 2 (or more) of the 12V power-supply
cables from a PC power supply together in series to get 24+V? It this
at all possible, or do peculiarities of the switched power supply
system mean that this is a PSU death-trap waiting to happen?

PC power supplies just seem so conveniant, with their handy 5V
logic.. if we could just get more than a wimpy 12V out of them they
would be quite good for most peoples CNC needs (connect 3 12V's for
36, or 4 for 48V!). Of course, some big capacitors would probably be
neccessary.. but where else can you get a 300W PSU with 5V logic for
$20. :)

So, is it a death trap?
Thanks!