I've done some scope plots for the problem on channel 3 and sent it to the support. It doesn't need to be a problem of the PSU in general, maybe my unit is just broken, but I doubt it. Maybe someone can verify it with his/her unit, if you have the same PSU?
![](http://www.frank-buss.de/spd3303d/power-on.png)
I loaded channel 3 with an 8 ohm resistor, then I turned the PSU on with the power-switch (the PSU was turned off a few hours before). As you can see, there is a 1.5V spike, falling down over some milliseconds (1V and 1ms per division). The voltage selection for channel 3 was on 5V. If I turn it off for just a minute, and then on again, the spike can be even higher, I've measured up to 7V. There should be no voltage at all, because the channel is turned off initially when I turn on the PSU.
![](http://www.frank-buss.de/spd3303d/power-off.png)
Same setup, this is what I see when I turn it off with the power-switch, and channel 3 still not enabled. A big 5V spike, falling over 100ms. And this is at 0,6A, because of the 8 ohm load. A sensitive DUT could be destroyed by it.
![](http://www.frank-buss.de/spd3303d/short.png)
Same setup, channel 3 loaded with 8 ohm, the channel output was turned on with the CH3-ON/OFF switch, and then I shorted the output. As you can see, there are some serious overshoots, up to 12V! If I have a sensitive DUT attached and accidentally short the power supply outputs momentary, it could be destroyed by such overshooting. I don't trust this output at all anymore, because maybe there are some other overshoots, depending on the dynamic behavior of the DUT.
![](http://www.frank-buss.de/spd3303d/short-ch2.png)
Just for comparing this with the other channels and to verify my measurements: same setup, but this time for channel 2 (8 ohm load, turned on). I shorted it momentary, as with the test for channel 3. As you can see, nice regulation without overshooting. Same for channel 1, no problems.