If someone faces the same prob.:
Error was not caused by wrong USB energy saving Settings (those were already set correct) but by wrong Drivers on the PCI/USB3 Card installed that came with the Driver Installation disk (most likely not suited for Win 10 anyway but for Win7, where same Card is working fine for weeks now.)
REMOVING the Card and anything connected to it including Drivers in device Manager then Research for new Hardware brought win10 to install ist own Drivers instead of the manufactures ones which - so far seem to work w/o any Problems.