[wtallis]

The voltage supplied by the motherboard isn't supposed to be constant. The CPU is continuously varying the voltage it's requesting, based primarily on the highest frequency any of the CPU cores are trying to run at. The motherboard is supposed to know what the resistive losses are from the VRMs to the CPU socket, so that it can deliver the requested voltage at the CPU socket itself. There's room for either party to screw up: the CPU could ask for too much voltage in some scenarios, or the motherboard's voltage regulation could be poorly calibrated (or deliberately skewed by overclocking presets).

On top of all this mess: these products were part of Intel's repeated attempts to move the primary voltage rail (the one feeding the CPU cores) to use on-die voltage regulators (DLVR). They're present in silicon but unused. So it's not entirely surprising if the fallback plan of relying solely on external voltage regulation wasn't validated thoroughly enough.