I'm Looking at the Rigol DP-831 Power Supply. The extra 2A on the first channel seem extremely appealing to me, though I see most people opting for the DP-832. Is the 3A limit on the DP-832 not an issue for most people?
Perhaps the 2A limitation on the other 2 channels is bigger killer?
Now that USB can hit 5A, I expect that we'll be seeing a significant increase in devices that get up to 5A in the near future.
On the supplies themselves, the DP832 has more power and is more versatile. the DP831's Ch2/3 arrangement as +/- is useful for some applications, but not as versatile as the two independent Ch1/2 30V/3A of the DP832, especially once you consider series/parallel arrangements (you can do 30V/6A with the DP832 Ch1/2 if you need more amps, which you can't on the DP831 with Ch2/3).
It would be nice to have 8V/5A on Ch3 of the DP832, I agree, but in many applications, 5A is pushing the cables and with no sense function on either, I'd say it is not a commonly used current level (and again, you can do 6A with the DP832 by using parallel mode if you really need to).
As for USB and 5A, I am not that convinced. 5A is only available with the newer type C power delivery and only with special active cables and devices at both ends negotiating 5A. If you look at current USB power devices (like type-C PD laptops and mobile QuickCharge), they all use high voltage (up to 20V) and 2A (sometimes 3A) current so that they can keep off-the-shelf cables. So I see 5A only used in laptop chargers needing to push 100W instead of 60W max with their own cable. It doesn't seem to be made for random USB devices and off-the-shelf cables (those will go high-voltage first).