As the topic sais I want to change a 12V rail to a 5V one on a PC PSU I have. The reason for this is that the PSU I have only has 12V lines (it's a PSU specifically for SLI setups), but I don't need as much 12V. I currently have a 300W passivly cooled PSU installed which barely pulls my system (server). As such I want to add a thermaltake Power Express 250W to take some of the strain off of it. However it only supplies 12V lines so I can't hook it up to for example the hard drive or DVD drive (or currently even the GPU for that matter as it wants molex). Now I'm not sure how to go about this however or if it is even a wise idea . Any resistor would be a bad thing not in the least because it would probably get hot as hell . So I guess I want to use a DC/DC converter but I'm not sure which one would be appropriate (and which wouldn't get too hot). Anyone have any ideas ?