Interesting, the ND555 picture on the Naim product page does show a power button, I had looked it up. Maybe they mixed up the pictures again and it’s an NDX2 
In this case, I suppose the manual would say if there was anything special to observe
Yes, ndx2 does have a switch.
Nothing in the manual about dual power supplies.
Thank you though.
You’ve done the same thing I did! The OP has an NDS not an ND555 
I’d email or call their technical support. Then please let us know what they say
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Great minds … 
Yes, I know that now about the NDS, but I didn’t know when I wrote my first answer about the power button, because he hadn’t said what he has and there is nothing in the profile
[Edit: It’s in the very first line. I overlooked it, sorry]
(And I thought if the ND555 has one, most likely an NDS would too. Bad assumption …)
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Thank you for your help.
Of no consequence, but I did say I had an nds in the very first line of my request for help.
I will email naim on Monday.
However, if anyone has experience of using two 555ps power supplies with any naim device, AND
they have NOT switched them both on at the same time.
Please tell us
Which supply was switched on first, and more importantly from my point of view
DOES HAVING A DELAY BETWEEN SWITCHING EACH SUPPLY ON CAUSE A PROBLEM.
Thank you
I have 2 non-naim power supplies on my NDS and it doesn’t seem to make any difference which order I switch them on in.
The NDS happily boots up either way.
I did spot it was an NDS but made the wild assumption that the ND555 would operate similarly. This based on, again a possibly wild assumption, that Naim would make it absolutely explicitly clear if switching on in a ‘wrong’ order was likely to damage either unit.
But what do I know…
G
MaxiMe
(and, to be fair, just about everyone else)
Thank you.
This gives me considerable confidence that
YOU DO NOT HAVE TO SWITCH THE POWER SUPPLIES ON AT THE SAME TIME
Sometime next week, I will try this and report back.
I did not know if it was safe or not having one part powered before the other or not - assumed a staggered-start powering would be OK with about 1-2 secs between ‘on’ whichever supply went first.
This worked fine for both CD555 and ND555 for the many years I have had the former and now the latter.
In short - just turn one on, wait a count of about two seconds and then turn on the other and it will all be fine. 
Most designs allow some time for things to become stable with muting relays and the like, which is usually several seconds, so do your on-sequence within that and it will all work fine.
DB.
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As an Electronics Eng. (retired) I was taught to switch on from source to end in order.The rationale being that you do not want to leave a high impedance input “floating” while the source’s output may be all over the place during power up. However, that lesson was nearly fifty years ago - OTOH, stuff one learns in “one’s yoof” does tend to stick.
Therefore in this case - digital then analogue.
You have explained much better what I was trying to say earlier, based on logic. I’m just a humble Zoology PhD though.
I was also taught to turn off every bit of power before fiddling with interconnecting cables, or poking one’s fingers into units.
Naturally being a (know-it-all) Elect. Eng., I have ignored that directive on numerous occasions.
I’ve even got away with it… most of the time LOL!
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If the Digital supply powers the output mute relays then you want Analogue on first to get stable then the Digital. Generally Digital has its own logic system to associated, with timers - Analogue systems use RC timers to give delays.
I have no idea what Naim do inside other than it all works however you power it on. I used to design and build electronic equipment for work and and have designed and built DACs for my own and friends use, so I also do know something of how all these things work.
Generally you want the Analogue system up and sitting ready before it gets presented internally with a signal or has non-stable output sent to your Pre. Digital is either ready working or not so is safer.
DB.
As Naim don’t specify it, I think you can be sure that it doesn’t matter at all either way.
I switch my 555PSs on one at a time. It’s a habit I developed in the days when Naim equipment had more of a tendency to blow fuses on switch on. Turning on everything in turn allowed me to check that each box had started. Only my 500 still has this tendency and it is thankfully occasional.
I have never seen a simultaneous switch on recommended by Naim in any manual or article. If it was a preferred or recommended procedure, Naim would say so. There is more of a potential to trip a switch if several boxes start drawing at the same time.
Harry
Thank you, just what I wanted to hear.
Just for the record, what ORDER do you switch the power supplies on?
Ie analogue (burndy socket 2) first, or
Digital (burndy socket 1) first?
Or, perhaps, either!
Everyone is confident that the order does not matter.
However, it has been interesting reading the suggestions as to why one might be slightly better than the other.
Thanks to everyone for the help,
It’s is much appreciated.
You are welcome.
My power on order is:
552PS (the 552 takes up to 30s to initialise so draws immediately but does not become operational).
555PS analogue.
555PS digital.
500PS.
These are stacked upwards, so I just push the bottom button, then work upwards.
So far as I know it makes no difference in which order they are pressed, although I was advised to turn on the 500 last. I remember that when the dealer last tore it down and rebuilt it, we discussed which box should go where on the rack for the best sound performance. We wanted the 552PS as far away as possible from the 552, and the 555PS analogue further away from the ND555 than the 555PS digital. Putting the 500PS one shelf under the 500 made no difference. I only have space for one stack, so this was considered the most optimised order for the space available.
The switch on sequence just arose out of the stacking order. Because I was advised to turn on the 500 last, I go up from the bottom. Powering up and down is rare. It’s been necessary of late because of thunderstorms and occasional flutters and brief on/off cycles in the mains supply, which can blow equipment fuses - we have spares. The mains has now been resolved.