USB Power Delivery (abbreviated USB-PD) was defined in 2012 to provide direct current (DC) voltage and current (power) to devices beyond the previous USB 2 specifications. 

Every normal USB-C cable must support at least 3 amps of current and up to 20 volts for up to 60 watts of power according to the USB PD specification. Cables are also allowed to support up to 5 A (with 20 V limit up to 100 W of power). However, the 20 V limit for 5 A cables has been deprecated in favor of 50 V. The combination of higher voltage support and 5 A current support is called EPR and allows for up to 240 W (48 V, 5 A) of power according to the USB PD specification.

For cables with up to 3A and 5A delivery, they can be used for

• Charging USB type C enabled devices such as cell phones and tablets. 
• Transferring photos and music between devices.

The biggest difference between 3A and 5A cables is 5A cables can generally power laptops and monitors while 3A cables cannot. 

The following is a table showing the labeling for speed and wattage to be used for modern (2025 and later) products (click the image to enlarge):

Updated USB logos will also apply to cables. Jeff Ravencraft, president of the USB-IF, said that was done to clearly communicate the only things consumers cared about: what data speeds the cable supported and how much power it could pass between two devices.

Check Wikipedia for compatibility issues.

Measuring Power Delivery

The ChargerLAB Power-Z KM003C Portable USB-C Fast Charging Tester PD3.1 QC5.0 Digital Voltmeter & Ammeter Power Bank Tester has been held to high regard as to showing voltage, current, and power and the ability to read E-Marker chips. The community states to buy from ChargerLAB/Amazon/known distributors as there are knockoffs. This is not an endorsement, just noting what has been stated online.