Got the same problem here… I have also been looking for another power supply but also couldn’t find it. I bought for really not much money on a webshop here in belgium this transformer and still had en plug conversion here from my last trip we made to mexico to transform it to american standards. It really made whisteling less but not totally quiet.
I found it nice of drobo to send met quickly a new power supply, but didn’t like it when I heard it whistled harder then the one I had. BTW, the first drobo fs I got, was exchanged the day after for this whisteling problem. The shop I bought it from was so kind to do this. So this power supply I got from Drobo is really already my third one :-).
So I think that they really have a problem here with this type of power supplies.
What I find disturbing is that they didn’t check the power supply they send to me on one of there drobo FS machines over there in Germany. Then they would have heard it.
It isn’t my machine that’s creating the whisteling because this is my second DROBO FS machine.
Is the power supply you have also MADE IN CHINA version ?