Jimmy wrote:

It is my understanding that PC powersupplies take 120 AC and run it
through a voltage doubler rectifying it and giving 300vdc. What I
want to do is feed 300vdc into the powersupply via the line cord with
no modification to the power supply. As I dont have a schematic could
someone please tell me if this would work

Warning!
what are you trying to dO? send smoke signals?
Who was telling you about 300vdc? to power up a PC?
A pc uses +5Vdc and +12VDc. so forget about your idea.