I'm aware it's common for computers to have booting trouble because of USB devices. I have the opposite problem. My computer will not turn on unless my phone is plugged in.
If I try to turn my computer (desktop, self built, a bit old) on without the phone (Galaxy S5 with a fast-charging USB 3.0 cord) it does nothing, not so much as a whimper. If the phone is plugged in to the motherboard (haven't tested the case USB ports), it works just fine. In fact, if I press the power button and THEN plug my phone in, the computer springs to life without my having to press the power button again.
I've had a few power supplies die before, but I don't think that's the issue this time. I have a lot of stuff plugged into one outlet (remedying this soon) so maybe it's electrical. I've tried unplugging a bunch of stuff to get it to start again, which didn't have any effect.
Is my phone and it's cord acting like a car battery and pair of jumper cables, bringing to life a machine that has enough power to run but not enough to start? Is it holding some sort of charge that says to boot up that it only responds to as soon as it can? Or could it be a simpler, less concerning issue? Like the presence of the USB fast-charge device messing up some baseline power value somewhere because I turned on my current power supply for the first time with my phone plugged in and it thinks that's what normal looks like?
Thanks for any and all help.