IN CPU

Not effectively.
Most electronic equipment retains some charge in its capacitors, this small amount of power could perform some trivial task after switch off, but I don't see how it could be harnessed to anything useful. In general if you extract residual energy you will only have to replace it next time the device is powered up. Often there are bleed resistors to avoid high voltages lingering too long for safety reasons. Aslo highvoltage desn't equate to high power.
Del
(BTW. I heard you the first time...)