My very 1st power cable experience a month ago is the same as yours. Plugged it into the amp first.... "okay". Plugged it into the dac simply because I was curious. WOW.
I’ve switched back and forth with the only 1 upgraded power cable that I’ve got, and always it sounded much better on the DAC. Here’s the strange thing tho, with the dac it was all improvements, so it made a huge difference.
With the amp, well.... hmm how should I describe this. Imagine putting a 500 HP engine into a 1990 Lexus. It felt like "fix your other priorities before you join the big league". It felt like the amp was having an effortless time separating the sound and magnifying the sound, But the sound had grains and digital glare, So I was hearing more of what I didn't wanna hear.
If you PM me, I’ll let you know how it goes when I receive my 2nd power cord that is going permanently into the amp, ETA 2 weeks.