I solved this problem. It was related to SD card indeed. None of OpenElec image wanted to work from this card. But I had completely no problems with different Linux distributions and also Androids via PhoenixCard. This SD card is still in my use - no errors. So there must be a bug in OpenElec bootloader or something related. Finally I found cheap but decent Class10 16GB cards and first time I could see OpenElec

Regarding power - according to Orange Pi PC schematics all USB ports should have Zenner diodes at data lines and power. Also DC socket is secured by Zenner diode. Unfortunately there are only empty spots on the PCB

From photos I can see that more expensive OrangePi models have these diodes soldered.
But I cannot complain - for $15 price it is real bargain. I have even purchased Orange Pi One and will Lite model too