You will need to unlock Electronics to unlock power generation equipment. Luckily, electronics takes red science.
it was a mod conflict :-( although i had reduced the mods to only two, that other mod just was modifying research techs too, and thus electronics only enabled fast inserters and long handed inserters, but nothing else.
now i have removed that other mod too and the electronics research that i already had done now really has boiler, steam engine, small pole and labs, BUT those items are not enabled for me since i had researched the tech before those items were part of the tech :-(
usually, such an effect happens when a mod is installed after a tech already has been researched, and then the problem is (or rather should be) taken care of by a migration file that checks which techs are researched and reset them so that the items belonging to that tech are enabled. in this case, this mod was not changed or installed and thus no migration would have been run, but the problem occured because of removing another mod that hid the items of this tech. i have no idea how this can (should) be resolved ...