when disconnected,

Hello.
I'm translating a sentence and it's bit complicated because there are 2 commas and I'm confused which one comes first.
I've been trying to understand the flow of the sentence so the commas wouldn't bother me but it's not working.

To make it clear, I would say
Device may only be adjusted by authorized experts - 1
when disconnected -2
and whilst observing the local safety and accident prevention regulations - 3

Device may only be adjusted by authorized experts, when disconnected, and whilst observing the local safety and accident prevention regulations.

Source: Device's manual.

Is your question whether or not the comma placement is correct? If so, the commas are indeed placed correctly.

I don't think that I showed what I want to ask.

I'm confused with commas and missing subjects so I want to know that I rephrased correctly.

When device is disconnected, device may only be adjusted by authorized experts and during experts adjust device they need to follow the local safety and accident prevention regulations.

Have I got it properly?

It is a logical AND. All three conditions must be met:

Device may only be adjusted:
1. by authorized experts
2. when disconnected
3. observing the local safety and accident prevention regulations

Your alternative reads as an explanation of how the device may be adjusted when disconnected, but when it is connected the restrictions don't apply - adjust away.