Recently I have heard about USB Kill, a device that looks like a flash drive, but completely destroys any computer it's plugged into by drawing power into capacitors and then pushing it all into the device at once. I have reason to be concerned that someone might try and use one of these devices on my brand new laptop. Is there a way to completely disable all power to the USB ports until I have unlocked the PC? To be clear, I don't want to permanently disable the ports, I want to be able to use them as soon as I unlock my PC. I am using Windows 10 Home 64bit.
It is difficult to speak for all laptops, but the usual design practice was not to use dedicated high-side switches to control VBUS on USB ports. The VBUS is usually tied to a general 5V voltage rail that is controlled by general power management on system wake-up, with exception of "OTG" or "charging" ports.
Therefore, given this diversity in hardware implementations, it is very unlikely to have the software work-around, even at BIOS level. Theoretically speaking, the general USB controller does have provisions to have the port VBUS disabled, and only be enabled when software "enables" a particular port. So the software should be ready to do the job. Unfortunately I have never seen host controllers (except USB hubs) who implement this native capability to control VBUS. Therefore the OP's question and idea is becoming really actual with proliferation of spying flash drives and the recent invention of "USB killer" devices.