Vintage preamp/amp power cords

I’m guilty, Furutech IEC AC Inlets and a dremel. Other thing to consider is a better wire on the internal side from the IEC too.
Was there an improvement once I added an upgraded power cord? I would like to think so...*grinz
Edit: Wanted to add, various power cord materials will give you more lows, highs, or a neutral affect.

One of my early mods long ago, replaced the factory cord. Only my approach was, long as I got the soldering iron out.... hardwired the new one in.

This was back when I wasn't really even sure it would make a difference. Now I would still recommend hard wire if you have one you know you have heard and know you will be happy to live with. Anything other than that you need to audition several, and that means iec.

Safety, unless you see signs of overheating or fraying or cracking, you can just forget that one except if it helps as an excuse to rationalize what you should be doing for sonics sake. Even something as basic as Synergistic Research Master Coupler will be a profound improvement. Hardwire one of those directly to wherever the existing terminates inside the chassis, huge improvement.

Adding an IEC inlet will not help anything. It will only add another point of (I^2)*R (or more precisely, (i^2)*z) power transfer loss. You will not want to put an over-sized power cord on your equipment either, as it lessens the ability of the power supply’s filtering circuitry to reject noise proportionally as the cord impedance drops (ie false economy).