DC power supply?

[James3]

What “myth” are you meaning?

FWs own document about the FW Desktop PSU backs up what I am saying:

Framework Desktop Deep Dive: Power Supply

[image] We’re close to the finish line on Framework Desktop development. We’re now at the end of the DVT2 phase where we complete validation and finalize firmware and drivers. With that, we’re continuing our deep dive series, this time digging into the semi-custom 400W Power Supply we integrated into the product. This may sound mundane, but it’s one of the more complex parts of the product. To align to our product philosophy, we used a standard FlexATX form factor. That means both that you can…

Quote from FW:
“Although the “peak” power demand of the AMD Ryzen AI Max processor is 140W, it can actually pull hundreds of watts in millisecond-level bursts. Because there is no battery in the Framework Desktop to absorb this, we sized up the Power Supply to handle it and maximize performance.”

Yes, you can use a laptop with just a PSU and no battery, but in those scenarios, the FW EC firmware applies a different, lower, power profile, to minimize the peaks. FW publish their EC source code, so you can check the source code if you don’t believe me.
E.g.: Extract from EC source code for FW16:

               } else if ((active_mpower < 100000) && (active_mpower > 0)) {   // Size of the PSU up to just less than 100W PSU.
                        if (with_dc) {  //  with_dc means the battery is attached.
                                power_limit[FUNCTION_THERMAL_PMF].mwatt[TYPE_SPL] = 60000;
                                power_limit[FUNCTION_THERMAL_PMF].mwatt[TYPE_SPPT] = 60000;
                                power_limit[FUNCTION_THERMAL_PMF].mwatt[TYPE_FPPT] = 60000;
                                power_limit[FUNCTION_THERMAL_PMF].mwatt[TYPE_APU_ONLY_SPPT] = 30000;
                                thermal_stt_table = 6;
                        } else {   // without battery attached.
                                power_limit[FUNCTION_THERMAL_PMF].mwatt[TYPE_SPL] = 30000;
                                power_limit[FUNCTION_THERMAL_PMF].mwatt[TYPE_SPPT] = 30000;
                                power_limit[FUNCTION_THERMAL_PMF].mwatt[TYPE_FPPT] = 30000;
                                power_limit[FUNCTION_THERMAL_PMF].mwatt[TYPE_APU_ONLY_SPPT] = 30000;
                                thermal_stt_table = 31;

I dare say that someone could modify the FW Desktop EC source code to make the power profiles compatible with a 250W PSU, instead of the FW 400W PSU, but it would be at the expense of slightly less performance in order to reduce the peaks.
I have not actually tested how much performance is lost by reducing the peaks or how effective the power profiles are at reducing the peaks.

It might be wise for the Original Poster to send a support request to FW support, for advice on DC powered PSUs. They like their products being used in unusual and new situations, so I am sure they would like to help.