Update: I've upgraded to the new firmware 48h ago. The rejected shares are down to 3.3% (96.7 accepted) and my average hashingrate is now @ 490 MH/s.

Edit: Looks like there is a new A10 Pro+ 6GB with 720 MH/s and 1300W available soon: https://www.whattomine.com/miners/126-innosilicon-a10-pro-6gb