In S3, the system controller powers down the CPU and nonvolatile storage while keeping RAM in a low-power self-refresh mode until you wake it up. Your operating system is not running -- the microcontroller that reads the lid sensor and power button determines when the laptop will resume.
In S0ix, the CPU is still running, and the OS kernel is supposed to put itself into a low power state most of the time, while periodically doing things like checking email and performing updates. The lowest power state still uses gobs more power than S3, and Microsoft is aggressively irresponsible about when and why it wakes up. It's more like "turning off the display and spinning down disks after inactivity" and less like a real sleep state. Windows is running the show 100% of the time, even when the laptop is in your backpack.
All this because Microsoft was jealous that Apple can check email and download updates without waking up using their T2 system controller and now their own SoCs. But Apple is way less aggressive about waking up, their firmware is generally pretty okay, and T2 still uses less power than an x86 in standby.
Windows, on the other hand, has to run on every PC, so they can't specify some crazy advanced system controller, nor does Microsoft have any control over the firmware it runs... Instead they had to ask Intel to add a new sleep state that puts Windows in the driver's seat, and in order to make sure it gets used and people don't "accidentally" get stuck using the "old" S3 sleep, they made it so that you can only have either S3 or S0ix enabled, so all system builders would essentially be forced to switch. Some (Lenovo) offered a BIOS flag to surreptitiously switch between S3/S0ix before boot time, but even that seems to be going away or broken lately.
I have to believe that this will get better eventually, if only because the current state of things is so atrocious, but I wouldn't plan on buying a new laptop in the next 2-3 years.
Or stuff another embedded core onto those enormous CPU dies.
Is AMD in a better place regarding sleep states?
As far as I'm aware, S3 and SOix both exist on AMD, but I'm not sure whether they can exist simultaneously. There seems to be just as much confused annoyance at power consumption issues on AMD laptops as with Intel, e.g. https://forums.lenovo.com/t5/Other-Linux-Discussions/P14s-Ge...
Not really sure what to make of that, but it sure is disheartening.
Separately, while AMD's better performance / watt would seem to make it a good candidate for laptops, lack of Thunderbolt across the board has also been frustrating, especially if you already have a nice TB dock setup.
It was the worst linux experience I've ever had, and just a bad experience in general. They gave it a broadcom wifi chip which has poor linux support, no built in drivers out of the box so whenever I reinstalled I needed to connect an ethernet wire with a usb dongle to download the driver. The wifi also just had very poor reception compared to other laptops.
Sound problems intermittently where half of the time it would have no sound on boot, and I'd have to continually reboot until it decided to work.
They had an absolutely infuriating feature which adapted brightness levels of the screen so that if you transition from dark to bright it would gradually adjust. Except this feature was broken and it does the opposite of what was intended -- it instantly cranks the brightness up to 100 and then gradually adjusts down to what the beightness should be. Even if this feature worked properly it would be undesired, but it is broken in the worst way and there is no way to disable it on my model. I have spent many hours trying.
The computer also arrived with the chasis mis-aligned. I couldnt plug anything in to any ports, we had to get a dell guy come in and reasemble the machine.
The charger also stopped working after about 1.5 years. I bought a new charger but now the charging port only works intermittently.
QA issues aside, you'd think that they would choose parts known to work well with linux but they inexplicably did not.
It's soldered in so can't be replaced.
This is a laptop I bought with Linux support out of the box but I've given up expecting Dell to fix it. It's easier just to kill off and restart the wifi connection when it stalls.
Given that I'm not sure I'd buy another Linux Developer Edition laptop from Dell.
But I also had several coworkers with the same newer 11-series XPS machines who got a series of lemons... Dell replaced the motherboards, but still.
I think that XPS build is just the wrong machine for Linux and like someone else said the wrong form factor for poor power performance management.