I'm planning a project that will be closely tied into a desktop PC, and I'm going to need some power both for the
spaghetti electronics and a whole bunch of fans.
Can I simply use the the +5V line from a PSU Molex to power the Arduino?
I don't need to worry about all the trickery of getting the PSU switched on, keeping it on, and so forth, because when the PC is off, my project is off. If I do end up needing always-on, I should be able to work out some shenanigans such as this project from Contesti.
I was going to connect the +5V line to the Uno's Vin pin. That is that regulated, correct? Or do I have to go through the edge barrel-connector to get through to the VRM on the board?