Old 19V laptop supplies are cheaper and more plentiful than 12V ones, so Im not surprised by ebay seller 😀
I dont think there is anything using 12V in this box. I think you correctly located the two possible problem points, measure if PCI A2 is even connected.

Thanks. It's late here, but I'll try to find time to check A2 tomorrow.

Is there anything to my concerns about straining the voltage regulation or pushing the limits of the case's ability to convectively cool itself?

I don't know what kind of voltage regulation it uses, but my reading up for five minutes of playing around with an Arduino half a decade ago taught me that, if it's using a linear regulator, higher input voltages result in more power being burned off as waste heat, so, for an Arduino Uno, all else being equal, 7V is better than 9V is better than 12V within the recommended 7-12V subset of the input range its regulator supports.

higher input voltages result in more power being burned off as waste heat.

More voltage equals less heat, because less current is required and efficiency of conversion is usually better, that if a VRM can handle it and nothing is feeding directly from 12V. Anyway, it's not a big issue to procure a standard 12V power supply.

its doing dc-dc for 5V, but it might be using 16V capacitor in front of it

The Serpent Rider wrote on 2024-06-08, 03:00:

Anyway, it's not a big issue to procure a standard 12V power supply.

It's a question of whether I should negotiate with the seller for a partial refund over whether this meets the "man on the street" definition of "(compatible)" for a power supply.

I don't know about where you live but, here, it's $20 + $5 S&H on Amazon.ca for the kind of power supply you'd expect to see being pulled apart on bigclivedotcom and all the sources for genuine high-quality supplies seem to want $20 + $20 S&H for this configuration. That's a non-trivial portion of what I paid for what was supposed to be the unit and a power supply I can trust to be compatible.

I just power my T5720 with generic 12V power supply from a spare external HDD box. T5710 requires even less power.

The Serpent Rider wrote on 2024-06-08, 09:38:

I just power my T5720 with generic 12V power supply from a spare external HDD box. T5710 requires even less power.

That still assumes I have a 12V supply where I don't also want to use whatever it came with... and that I consider it reasonable to have paid a price on the assumption that I'll have a use for the included power supply when I already have more 19V supplies kicking around with no use for them.

Yeah, I'm definitely not considering the supplied PSU "compatible". All the capacitors are rated 16V except for a couple of small ones in behind those big green ones which are rated 6.3V.

Unless HP designed a DC-DC converter with no capacitors on the input side, the only reason the seller hasn't blown one of these things up by feeding 19V power into it is that HP picked capacitors with enough of a safety margin to account for degradation with age.

The barrel jack is in that gap behind the rightmost tall, green capacitor.

Of interest is that the later HP t5740 is actually spec'd for 19V and uses the same connector as the HP laptop power supplies. I picked up my t5740 without a power supply and it was easy to find a compatible power supply for it. (This thread did inspire me to go check the t5740's spec sheet to make sure I wasn't inadvertently dooming mine to an early death!)

The Serpent Rider wrote on 2024-06-08, 03:00:

higher input voltages result in more power being burned off as waste heat.

More voltage equals less heat, because less current is required and efficiency of conversion is usually better, that if a VRM can handle it and nothing is feeding directly from 12V. Anyway, it's not a big issue to procure a standard 12V power supply.

I understand where you're coming from (the same reason 240V countries can use less copper for the same wattage rating when wiring a house) but I was talking about the inner workings of a linear regulator.

What I was referring to when saying "All else being equal, 7V is better than 12V in the recommended 7-12V range for powering an Arduino Uno from the barrel jack" is the VIN – VOUT in the PD = [(VIN – VOUT) * IOUT] + (VIN * IGND) power dissipation equation for linear regulators as laid out in https://www.maxlinear.com/files/ApplicationNo … /LDOThermal.pdf.

With linear regulators, heat dissiptation requirements can be crudely thought of as "burning off the excess voltage".