The little DPS3003 power supply module arrived today, and onto the bench it went!
On the good side, it actually cleans up the noisy output from the Toshiba laptop power supply I am intending to use with it. In all photos, the top trace is input voltage and the bottom trace is output voltage, both AC coupled. In the first photo (3V_1A24.png), the output voltage has been set to 3.0V into an incandescent lamp load, yielding output current of 1.24A. In the second photo (12V_2A48.png) the output voltage has been increased to 12V with the current going to 2.48A. While the output noise does rise a bit, it's nowhere near linear - the 3V DC output shows 4.38Vpp of noise (!!!) while the 12V DC output shows "only" 5.43Vpp of noise.
3VNoise.png shows a closer view of the relationship between input and output noise, and 3VNoiseZoomed.png zooms in on one of those spikes. The little supply module does what it can, and it actually does cut the input noise to some degree, but the high frequency content is too much for it so a lot gets through.
Next up: How it looks with a clean(er) source of input power. If it looks better I might be able to use it for my backpack power supply, but if it's still noisy the hunt will have to resume. I really want to like this little module... it's almost perfect from a functionality standpoint, and with a quick 3D printed enclosure it would be very travel friendly. But it's got to have clean DC out....
UPDATE: Tried it with a GPE-4323 bench supply. Cleaner, but it's evident that the noise in the photos is not just laptop switcher noise, but also this little switcher module's noise - at the input and the output. I am revising my earlier opinion that the noise at the input is from the laptop switcher; I'm now convinced it's input-coupled noise from this little module. At the input, you can literally see the PWM duty cycle vary as the voltage is varied. At the output, the noise is pretty much the same as with the laptop switcher. At 12VDC out, the noise is just shy of 4Vpp at ~65KHz. Pretty nasty for a DC power supply, so the hunt continues.