27
Dell PSU is “PD3” but cannot do PPS. Isn’t that non-conformant? OTOH, there is no USB-PD indicator to begin with. (thelemmy.club)
submitted 3 days ago* (last edited 3 days ago) by to c/askelectronics@discuss.tchncs.de
12 comments fedilink hide all child comments
 

I am trying to get a grasp of how to identify what power standards various PSUs claim to conform to. The label on this Dell PSU is ram-packed with info, but I see no direct claim that it supports USB-PD at all.

The range of voltages might imply that perhaps maybe it’s USB-PD, but I see no indication where they take credit for that; much less a particular PD revision. IIUC, that means if it’s USB-PD non-compliant and someone drags Dell into court, they can say to the judge “we never said it was USB PD-compliant”.

The review that probes this thing shows that the PSU is detected as PD3.0. Yet at the same time it does not support PPS according to the blogger. So wtf.. how can it be PD3 if it does not support PPS?

It seems Dell is banking on consumers not being keen to read the label. According to the blogger:

The odd thing is that it is advertising itself as a 96W adapter (20V/4.8A) which is different to the printed 20V/5A rating on the rear.

So it seems has Dell decided that if they do not benefit from advertising a capability, they might as well not mention it and downplay what it can do, for legal purposes.

The blogger goes on to test it with all kinds of fancy costly gear that no typical consumer would have. When I am at a street market rifling through a pile of dumped electronics, how do I know what I am looking at? Do any of the cryptic symbols on that Dell label suggest USB-PD?

you are viewing a single comment's thread
view the rest of the comments
[–] [S] 2 points 2 days ago (1 child)

I appreciate the link. I wanted to see what you saw, so I opened the ZIP file and it expands to 27 files. I believe the relevant file is USB_PD_R3.2_V1.2_2026_05_20.pdf, page 42, which states:

3.2.5.2. SPR Programmable Power Supply (PPS) Programmable Power Supply (PPS) is Optional. When included, the voltages and currents a PPS Shall support are as defined in Table 3.4.

If it’s optional in rev. 3.2, I assume it’s optional in rev 3.0. I’m a bit astonished because PPS is probably the most signficant feature of rev.3. The industry is not competent enough to even tell consumers which rev a device conforms to. But if it did, typical Wikipedia-informed consumers who see PD “rev.3” advertised would naturally expect PPS. As you are correct that PPS is indeed optional, many consumers will get burnt by the misunderstanding.

A potentially interesting follow-up question would be whether the laptop’s mainboard PDO tells you the laptop supports PPS even though its power brick doesn’t.

What’s PDO?

The problem seems to be that a laptop could be designed to /need/ PPS, e.g. if the voltage it needs is well below 20v. While most PSUs do not advertise USB-PD 3(+) compliance, much less PPS.

  • permalink
  • fedilink
  • source
  • parent
  • hideshow 2 child comments
    •
  • [–] 2 points 1 day ago

    What’s PDO?

    Power Data Objects are sent by the device to the host (in this case your power supply) containing information about device capabilities and requirements.

    The problem is that a laptop could be designed to /need/ PPS

    This would be highly unusual, especially for a Dell workstation laptop. Some laptops can use PPS for better internal power efficiency and battery charging rate, but I know of none that require it. The feature is also leveraged far more often in small sealed devices where waste heat has basically nowhere to go, so if any device were to actually require it, I would look to small wearables. In fact, while I haven’t checked and don’t know, I’d wager many smart watch chargers are PPS enabled, which would explain their oversized connectors.

  • permalink
  • fedilink
  • source
  • parent