I would like to power my ESP32 with a SATA powercable but I am not sure if a PC-Powersupply is stable enouth for that. The 3,3V would be perfect for that and additional I could use the 12V and 5V too.
Is it possible to do that or is it to unstable?
That would be fine; why do you think a PC power supply would not be stable enough?
Because no device which I know uses the 3,3V of the SATA powerconnector. They just regulate it from the 5V down to 3,3V or another custom voltage. I rode that it may have problems with the stability. But I guess the main reason will be money as usual xD. But I would like to know for sure before try to mutch with the sataport. And just use the Molex 4 Pin connector with 5V and 12 V.
It will work just fine as mentioned. The ATX PSU design guide calls out the specifications for all of the voltages and the 12.00, 5.00 and 3.30 volt outputs all have the same +/- 5% allowable tolerance. Everything you could ever want to know about an ATX form factor PSU can be found in Design Specification assuming the PSU meets the design specifications.
Ron
A bit of caution, some power supplies require a minimum load be sure to check the one you will be using.
Is there a way to make it universal usable so I do not have the load problem?
Is this still an issue? I haven't seen it called out in close to 20 years.
I haven't seen a need for a load since about 2004. I have an old Corsair CX550 sitting here which requires no load. When a load was required we used a 10 Ohm 10 Watt sandstone resistor on the 5.0 Vout. line. There are dozens of web articles out there on how to do it. The PSU I cited is about 15 years old.
Ron
The op never said it was new. The ATX specifications were released in 1995 by Intel and have had several revisions since. If it is an older one this could save a lot of grief and replacing of parts. Yes I have several that were that way but not only for the PC. They worked mainly by the turns ration with the main secondary being controlled the others following along. We also know not all were built that way but would work with a resistor on the 5V side. Better safe then sorry!
I got some PSUs which were from Pentium 4 PCs ( should be 3 ). The newer ones are build in to my PCs so I can test it there too.
I would like to use that device on different PSUs so it would be great if I do not have to change something when I use multiple devices on different PSUs
Regardless of PSU when we think about it it won't hurt anything hanging a 10 Ohm 10 Watt resistor on the 5.0 volt out line(s). The resistors are inexpensive enough and needed or not this will only add less than an amp load. Actually about a 0.5 amp load. Again the PSUs should output +/- 5% on the 12 volt, 5 volt and 3.3 volt outputs. PSUs already installed can have their voltages tapped into as long as we don't exceed the PSU ratings.
Ron