It doesn't matter which channels you try to parallel on the DP832 - it won't do it. You will have significant cross-currents and voltage drops. Believe me, I've tried it. Simply doesn't work. Get a supply with sufficient output or that can parallel outputs.
I can't tell about all power supplies, but Rigol can only source current, it can't sink current if voltage on its output is higher than Vset. So output voltage will be maximum from both channels (when current is low).
In general there can be several cases (assuming both channels are set to 5V, 3A) -
- I < 3A - both channels work in CV mode, output voltage is max from 2 outputs, the channel which have > voltage sources most of the required current.
- I > 3A but < 6A - one channel (which have > voltage) can't keep voltage and works in CC mode, supplying all 3A it can, second channel works in CV mode.
- I = 6A - both channels work in CC mode