A typical 30V Power Supply Unit uses a transformer and rectifier to produce more then 30V, in your case it looks like 48V. The PSU then either has some form of electronic stabiliser to accurately reduce the 48V to 30V or it relies on the fact that as you draw current, the voltage will fall and at the rated current the output volts will be 30V. As you say that the unit does not work use a multimeter and trace where the 48V goes to, because it looks as though there is a break in the circuit.
Frank