Let’s talk about the two ends of USB-PD as sources and sinks:

• A SOURCE provides the power. This could be a “wall wart” cube, or a USB powerbank battery.
• A SINK is the device being powered…a phone, a tablet, or whatever unconventional thing you’re looking to run this way.

USB-PD is a conversation…

• All USB Power Delivery sources use a USB Type-C connection. However, not all USB-C ports (source or sink) support USB-PD. It’s a specific subset and is sometimes labeled near the port.
• Here’s a whole guide on the ins and outs of USB-C. It’s deep.
• USB power between source and sink is negotiated. Unlike USB-A where current limits were expressed through passive resistors, there’s a bit of “smarts” at both ends of USB-PD. Lacking this at one or both ends, the most you can expect is 5 Volts at 3 Amps (and sometimes less than this…5 Volts certainly, but lower current).
• “Charge only” USB-C cables will not work work for USB-PD; lacking data wires internally, power negotiation can’t occur and the 5V ≤3A limit takes effect. One must specifically use a charge and sync cable. Thus, all three components — source, cable and sink — need to be the right type to unlock USB-PD’s potential.
• When fully compatible end-to-end, a USB-PD sink can specifically request higher voltages and/or current from the source: the specification allows for 5V, 9V, 12V, 15V and 20V at up to 5 Amps (and the latest spec has up to 48V!).
• Not all sources can provide all of these voltages! Many offer just a subset (more on this below).
• 5 Amps is the upper limit defined by the specification, but many sources are rated lower than this.

A USB-PD trigger unlocks these hacks…

• A USB-PD trigger (sometimes called a USB-PD decoy) is a small circuit that handles the USB-PD negotiation and simply outputs a DC voltage; one’s DIY project doesn’t need to handle the low-level details.
• Adafruit's version is the Adafruit USB Type C Power Delivery Dummy Breakout - I2C or Fixed - HUSB238.
• Some USB-PD triggers are adjustable with a selector switch, or cycle among voltages with a button press. Others operate at a fixed voltage, or will have solder jumper pads or a spot to install a resistor to select a voltage. For most DIY projects, the fixed voltage type is preferable, as this prevents mistakes that could destroy a circuit.
• The output on these is typically just two bare solder pads, or sometimes screw terminals. So you may be adding your own DC barrel connector, or other times might retrofit right into a device such as an old boom box. There’s usually some soldering and possibly some drilling or rotary tool work involved.

A Simpler Trigger Alternative

12 Volts is not universally supported…

• Not all USB-PD sources support every voltage. 12V — an exceedingly useful voltage in retrofitting projects — is an optional part of the specification. Even among esteemed brands like Anker, 12V is not guaranteed.
• If a requested voltage is not supported by a source, it will instead provide the next voltage down…e.g. one might ask for 12V but only get 9V.
• The list of voltages supported by a source isn’t always clearly shown on a product page, and sometimes not even in the manual! Available settings are marked on the source…usually in frustrating, microscopic, low-contrast type. USB-PD is a consumer-focused technology; the average person won’t care about Volts or Amps and would rather find their phone or tablet in a list of supported devices. So these hacks may require a little detective work before making a purchase.

• Some devices can operate at a lower voltage than “officially” rated for. A 12 Volt DC fan usually can run fine off 9 Volts, just a bit slower and quieter. Likewise with a 24V fan at 20V.