Well, now I know why the "scary reviews" are there. Heck, I'm amazed why there aren't more of them...
Well, if it works for you then... it works. Just keep the two PSU as far as possible from each other. For example, if a GPU had 2x6pin power connector, then connect both connector to the same PSU, do not split. Also make sure both PSU are turned on/off at the exact same moment. Most modern GPU put the 75W PCIe power to their own VRM section, or join the rail through sensing resistor and/or MOSFET switch, so I guess that's why the magic smoke didn't get released more often...
Personally, I still won't test my luck doing that tho...
I wonder if the Dell PSU is ATX compliant. If yes, then just replace the PSU altogether. Less hassle, less chance of magic smoke! probably better noise/efficiency/regulation too...