New Power Cable on a 1990 Hafler DH120?

Does it have an IEC connector? If so, it is Easy to start with a generic one off ebay for less than $50 and see if you hear a difference. read the fine print to make sure it is 10ga. I like the woven GR research cable.   I think just about all amps benefit from a larger power cable unless the power supply is choked by a long 14 ga wire in the wall or a power conditioner.

If you want to experiment buy an IEC outlet. Cut off most of the old power cord, leaving several inches. Strip the two conductor ends. Attach each copper conductor to a screw terminal on the back of the IEC outlet. Now you can use any power cord with a male IEC connector. 

@carlsbad : those old Hafler SS amps/preamps were made before IEC outlets were in common use. I have a Hafler 220/110 pair - both with captive AC cords.

The sound of an electronic component starts with its power supply. NOT with the wire connecting it to the AC outlet. If you believe otherwise then I recommend joining the Flat Earth Society.

The FES has chapters all around the globe.

Except for Australia…
https://www.theflatearthsociety.org/forum/index.php?topic=63521.0

     The local Master Of The Deluded ("Trust ME, I’m a fictitious operative!"), recommends joining a delusional, "Society".

                                      Reverse psychopathy?

                                              Projection?

                                           Either or both =