Looks like 12V was specified in PD 1.0, but I can't see it mentioned in the PD 3.0 specification. (Well, in the various extracts I could find online. The full spec must be published somewhere?!) Anyway, I don't mean to argue. Rigol decided to go for 15V, for whatever reason, and the scope obviously run on either 12V or 15V.
Oh, I wasn't trying to argue either. Just offering what I'd read from the specs as clarification.
Reference:
USB PD Spec Revision 3.2, Version 1.0, 2023-10 (yes, the ink is still wet)
The fixed compliant voltages (5, 9, 15, 20) are described in section 10.2.2 "Normative Voltages and Currents" on starting on page 1038. This the mandatory part (indicated by the directive "...
Shall support...") The SPR AVS (Adjustable Voltage Supply) part of the spec describes the ranges that supplies can optionally support. Section 10.2.3 "Optional Voltages/Currents" on page 1048 indicates two categories:
"Optional Normative Fixed, Variable, and Battery Supply" includes the statement "
May Optionally supply additional Voltages and increased currents. However, the
Optional Voltages
Shall Not exceed 9V."
"Optional Normative SPR Programmable Power Supply" (aka PPS) states "The Max Voltage
Shall Not exceed 21V while in SPR mode."
12V isn't called out specifically as it falls within the acceptable PPS range. Technically, a source and sink could negotiate 13.2V or any other odd value within the acceptable range as long as they meet the power constraints.
Section 10.2.2.2 (pages 1045-1047) describe the valid AVS operating ranges for different power configurations.
Example:
Pages 1049-1050 list examples of "what a power adapter that Advertises a particular PDP Rating
May offer:"
2) PDP 36W implementation includes:
o 5V @ 3A,
o 9V @ 3A,
o 15 @ 2.4A,
o SPR AVS with 9V – 15V @ 2.4A,
o 9V Prog @ 3 A, and
o 15V Prog @ 2.4A.
There is an example of 12V negotiation specifically mentioned in the B appendices (pg 1069-1070, pg 1074) where various example negotiation scenarios are described, including a Tablet that attempts to negotiate 12V:
And a laptop negotiating with an attached USB hub: