going to, problem is that the socket/outlet is not grounded.. so I'll have to fix that first.@fietsenrek
Don't trust the powersupply.
The humming sound is made by the transformer or the FET in the supply.
There is a oscilator circuit that feeds the FET and the FET feeds the transformer. The sound is the oscilator what you hear.
This humming is mostly caused by bad caps.
Buy a new (good) one .