Substitute, if you can, another IA and cdp without the power strip into your system and see if the problem is duplicated to confirm a power problem. But I don't think it's an A/C issue...
It's very possible it's the receiver (I'm assuming you reterminated with correct polarity). Could be worn out power supply capacitors, especially after 25 years. Other possibilities are damaged cable terminations or a problem with the input/output jacks on the receiver. See if lightly tapping or pulling on the input and output cables near the back connections result in a popping sound. Or try tapping on the volume knob and see if there's static/grunge.
It's very possible it's the receiver (I'm assuming you reterminated with correct polarity). Could be worn out power supply capacitors, especially after 25 years. Other possibilities are damaged cable terminations or a problem with the input/output jacks on the receiver. See if lightly tapping or pulling on the input and output cables near the back connections result in a popping sound. Or try tapping on the volume knob and see if there's static/grunge.