Strictly speaking 3A 5V is not part of USB-PD and so I do not know what would happen if I connected a USB-PD charger, it might say as its not profile 2 or 3 of 4 it defaults to common denominator of Profile 1
So you see the problem, I have a non USB-PD Powerport4, it gives upto 2.4A 5V. I have metered my Pixel C and from a 3A non-PD charger it draws 2.6A, from a non-PD Powerport2 I draws 2.2A.
USB-PD is 2A 5V or 12V 1.5A and the Pixel C is not 12V 1.5A capable therefore it may fall back to 2A 5V which is lower than what the Powerport4 gives. So it might be the case I have a step backwards.
The negotiations to common denominator is my biggest concern. Ideally if it said it can't do 12V it would then offer 5V 3A, not 5V 2A and let it draw what it needs.
We see this problem now with the Anker Speed systems, sometimes it negotiates a common denominator which is worse than other chargers.