Is it dangerous to connect multiple ASICs from one PSU?
it's the other way around. it is dangerous to connect multiple PSUs to a single ASIC. you can connect as many asics you want to a PSU as long as both your PSU and the 6pin connected can handle the power needed. from a theoretical point of view you can have 4 z9 minis connected to 1 APW 1600w psu ( each z9 mini takes about 350w if not overclocked" ). how ever i would not do that until i verify that the 6 pin connectors which are going to be split can actually handle the load.
https://bitcointalk.org/index.php?topic=1739630.0
You don't want to run your engine on max RPM to loong.
It's the same with PSU's.
this is completely based on your own or someone else's speculations and it has no solid proof what so ever, the max you see on the label is the safe point which a good psu should handle all day long. I have been pulling about 970w of a 1000w psus on my rigs for years and zero problems, it all comes down to the room ventilation and the quality of your PSU. bitmain psu is a solid psu. i have some A3 and S9s slightly over clocked consuming close to 1500 for ages and never a problem with the PSU. you can test it out yourself if you like.