My mains voltage is around 210-230VAC@50Hz (the switch at the back of the unit is set to the corresponding position). Not sure about the quality of the actual sine wave though, but I could check it using an oscilloscope. In addition I can try feeding the unit with 110-120VAC@50Hz to bypass H8000's internal converstion circuitry (if any) and see if it has any effect.
Also, I'm not sure if I have the third (ground) conductor of the IEC C13 plug properly grounded. Most probably it's just not connected.