I finally got around to measure the voltages of the PS-3500.
nominal | measured
==================
+15,00V | +14,96V
-15,00V | -14,99V
+12,00V | +11,87V
+08,00V | +08,04V
+48,00V | +47,89V
I couldn’t notice any 50Hz ripple as there was too much HF (in the range of about 20mV) from my computer...