What power supply do I need for the Raspberry Pi 5, can I use a previous power supply, and does it support USB-PD ?

Question

I've heard that the Raspberry Pi 5 needs 5v, 5A, what does that mean with USB-PD and can I use a previous power supply? How does this work?

cstanton · Accepted Answer

The Raspberry Pi 5, to take full advantage of the processing capabilities and features, and to supply 1.6amps to the USB ports, requires a 5 volts, 5 amps USB-C power supply. 
 The Raspberry Pi 5 official AC adapter is 27 watts (27w) and is effectively a custom USB-PD (USB Power Delivery) power supply that can negotiate 5.1v 5a, 9.0v 3a, 12v 2.25a, 15v 1.8a. 
 The Raspberry Pi 5 can be powered from 5v 3a which is typically negotiated from a USB-PD power supply, if this happens the USB ports will be power limited to 600ma (milliamps) as opposed to the full 1.6 amps. This can be adequate for most applications. 
 Negotiating 5v 5a is not typical from USB-PD power supplies and it is supported by the 27w USB-C Power Supply from Raspberry Pi. It uses 17awg captive cabling. 
 The Raspberry Pi 5 will not negotiate higher voltages (such as 9v or 12v) even though the power supply can provide it to other devices. 
 To use the Raspberry Pi 5 at its fullest you will need a USB-PD power supply that can provide and negotiate 5A at 5V. 
 Previous Raspberry Pi power supplies do not supply this. 
 You will also be able to add a line to the config.txt of the Raspberry Pi to tell it to ignore the USB-PD auto-detection and assume that the power supply can provide 5v and 5A.