>
>Is this hypothesis correct?  Are there potentially bad effects even if
>the +5 rail is heavily loaded?

yes, this is a bad idea.
if the 5v rail becomes lightly loaded, the fan current will be supplying the power, and the voltage will begin to rise. hopefully, the power supply will then throttle back, and fall into shutdown.

you obviously can get away with it, most of the time, but you'll not be plugging that mess into my pc.

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