Like always I would like to distance of any responsibility for advises I give but here is what I would do.
So you only though that it tries to boot when in AC and not connected to PC? Okay well look I would ignore the buzzing if its not a big issue (like loud and makes you go crazy about it) and just try if it actually works. Trying it out should not make things any worse if there is not like some smoke or you hear some electricity noise, it should not hurt PC you would connect it to.
Just don't leave it plugged in when going outside or something like that if there was some hidden problem, so you won't burn out, try to backup files somewhere else and if it works I would use it.
If you are worried tho, you can still backup and make a complaint to supplier to switch it for new if you still have warranty.
I hope I understood correctly my English is not top-notch and yours seems to have same problem so maybe we are misunderstanding each other atm.
GL