What so special about Sonic Frontiers ?

I have been having rather perplexing experience.
I am on my second Sonic Frontier Power 1 amp and it is the only amp in my system that sounds absolutely quiet and powers up very clean.
I also have had some other amps; tube and solid - and they all would exhibit some "issues" that seemed related to power source. Some units would generate pop when powering up, some would generate hiss and some others this deep humming sound like power lines.
SF Power 1 is the only amp that never gave me any of those symptoms.
Is there something unique in the construction of those amps?
Is it that my power line is really bad but other amps are much more susceptible, while SF 1 is just “resistant” to power related issues?
I never tried plugging power conditioner and always run the amps directly from an outlet.
I am looking to upgrade soon but worry that anything I try will again either hum with white noise or pop every time I turn it on.
Certtainly nothing special about the sound. I briefly owned a Power 2 and it was on of the worst sounding amps, SS or tube, I have ever owned. Was glad to see it go.

It is well-known that SF gear used very good parts quality and build was excellent. However, I personally had some issues with their Line 1 preamp and on one occasion, with a Power 2 amplifier.

Overall though, there is much to like about SF gear, I would own it again in an instant although more recent gear sound more transparent and resolving in my opinion. I recently compared an Ayon Orion integrated to a Line 2 - Power 2 SF combo - The SF had it on power, but everything else sounded much more refined on the Orion.
Sorry, should have clarified; I am looking for input on the build or parts of SF or anything else that would help me figure out why, up to this point, it is the only amp that is super quiet and doesn't make any weird noises in my setup when powering up.
For tube amps, its all about the following:
Placement of coupling caps so it doesnt become a microphone for the high currents supplying the filaments.
Careful attention to grounding and floating certain parts.
and a good startup circuit that warms up the the filament before operating B+ is fully applied.
SF power 1 and power 2 are wonderfully designed amps.
Just that voicing misses the mark with ultralinear.
Thanks for the feedback.
I will be reposting in Tech Forum.
Yesterday I spent about 4 hrs with 3 different amps, including the SF1, doing various outlet configurations.
Again SF1 was most "resistant" to any inpact from being plugged into different outlets or different conditioners, but I was also able to eliminate the problem with other amps (which I have been experiencing up to this point) by plugging it into a different outlet and also pluggin my pre-amp into yet another outlet...
I felt the same way as Shakey about their line 1 preamp. Not my cup of tea!