Bel canto monoblocks and power cables

For those, like me, who believe power cables make a difference: anyone with experience with bel canto amps and power cables. I use Nordost Vishnu with all of my source equipment and hear significant improvement.  With my BC ref 500m monoblocks, which I love and which sound so good, power cable swaps don’t seem to make a difference.   I’ve tried Nordost and Acoustic Zen Tsunamis. They don’t degrade the sound but there doesn’t seem to be much benefit either.  Anyone?
I have also found that with a really good audiophile quality amp I don't hear a noticeable difference or perhaps just a tad of difference when trying different high-quality power cords. In this particular case, I'm talking about my Plinius SA Reference amp.  I do hear a significant difference with my preamp, phono preamp, transport, Dac, and FM tuner.
We need someone like @almarg to explain this.
I've been experimenting with power cords and interconnect cables lately. Several manufacturers told me the most impact will "usually " be found by upgrading the power cords at the source and using the best interconnect at the source. 
I have ref1000m amps. These draw a lot of current when powered up not so much after. I use basic cords on those. Higher grade shielded cords on source gear. The amps power supply seems designed well to have power in reserve when needed. So I have not felt a need for beefier power cords. The amps are very efficient sound great and never break a sweat. Beefier cords not needed as much in some cases compared to others. Devil is always in the details.
i have 3 ref 1000m amps across my front in a HT configuration. I have used Crystal Cable, Siltech and now Purist Audio Designs (Neptune). I can def attest to a change in the tonality as i moved across the power cords.

it may be that the power cords you have chosen actually sound similar and therefore you didnt hear much difference. 
@thomaswv - Like you, I found good PC’s on my NAIM amp did not make an immediate noticeable difference - I had to find the right track that made the improvements more noticeable.

Those improvements are the micro details of the venue acoustics - now I know what improvement power cables make it is easy to hear and noticeable when you change back to a cable of a lessor ability.

I use the following DIY cables that I have compared to a few high priced products and found the others lacked the bass dynamics (slam) and very fine details of these

Check them out - despite their apparent complexity, they are pretty easy to build

Regards - Steve
Yes power cords can make a difference. But which ones? The only way to know for certain is to try them in your system. 

Consider going to read about their lending library. 

Also see  JPSLABS .com  Their cables are excellent. 
Thanks for the input. I’m going to try something I’ve never done...go backwards after a tweak, try the monoblocks again with stock cords. I absolutely hear a difference with sources, but with these particular amps I’m just not sure.  
@tomaswv  - listen for the venue acoustics in a live recording, such as a classical piece - preferably with 4-6 instrumentalists.

You should hear more echoes and reverberations and background noise.
e.g. in one recording I can now clearly hear trucks in the background.

With standard power cables it will be less pronounced

Good luck with your quest - Steve
Thanks to all for the insight.  I tested all three again--there was indeed a slight improvement over the stock cables. With the stock cords, the soundstage narrowed slightly--like one foot--and there was a little realism/vibrancy missing from Ravi Coltrane's sax on Alabama (front In Movement).  The Nordost and AZ were almost identical -- I went with the Nordost for now but could easily live with either.  These are Heimdall IIs, whereas when I chose the AZ over Nordost a few back they were Vishnus, so that may account for my current choice. At least for my Bel Cantos though, only a very slight improvement over the stock cables. 
When you have reference equipment,and I also include professional grade cabling in that context,the sonic differences are very subtle and as always it is more about synergy with your components.