Hey, i finally managed to change my whining PSU. I bought a Sunpower SPS 060-D1, which provides 5V 8A and 12V 4A, which is more than enough for the Central. Its a fanless PSU for internal use, and my Central works supersilent now.
I connected it to the HD and CD power with a Y-cable, from which i cut off one of the connectors, so i could connect the cables to the screw-terminals of the PSU.
Easy job, such a shame, that i didn't do that earlier.

cheers, Thomas