Tried 3 different ESP-12s, batteries or other supplies, different connections to CH_PD,GPIO..., with and without adapters, from a Mac, from a Linux box,... I've now spent 2 weeks on this and nothing. I am getting so frustrated!!!!
Especially since I can take one of these and all is uploading fine!
So what's different? What haven't I looked at?
About the print gibberish, yes, it is at 76800, but personally, with my USBSerial based on PL2303, I've never been able to get into this baud rate, but it didn't prevent me to do development. (I wish that Expressif avoid this baud rate forever, but I think they wish that we read it as chinese at boot up )
What did you upload as firmware ? Did you try some LED blinker sketch using ArduinoIDE ?
Maybe your board works just fine, but the thing you are putting in is just not good ...
And I don't own a Windows machine I could try uploading on.