I'm glad I could help you. I hope you won't have any problems. About the risks of using two power supplies, I meant that when powered from two sources, there can be two situations dangerous for your equipment. 1. Inside the Tesla K80, in the system for forming the phases of the processor's and memory's power supply, current can begin to flow from one of your power sources - the card box to another - the C6220 chassis. A voltage difference of 0.1V is enough for the current to be up to 10A, which can damage the device. In mining systems, different cards are powered from 2 different sources ALWAYS completely slot + card connectors, a slot from one power supply, and connectors from another - they do not do that, communication with the board is only through the card control lines and the Common chassis wire. When the riser is powered from one source, and the card itself from another, the card may burn out. 2. In the same way, the power system inside the card is connected, and the current from the card can start flowing into your C6220 and damage the board components if the power supply voltage of the box is even 0.1 V higher, 0.5-1 V higher - it is deadly. Or vice versa, current from your C6220 may start flowing towards the box and disable it. I hope you will be fine, but be sure to very accurately control that the supply voltages of your C6220 units and the box match, and be prepared to turn off the equipment very quickly if there is a smell of hot plastic. And turn it off by pulling out the power cables, if you turn it off with the button, you may not have time. Better yet, control the heating of the systems with a good thermal imager and if overheating is more than 70 degrees Celsius, turn everything off immediately. And never let it heat up more than 70 degrees Celsius - the internal structure of processors and memory begins to deteriorate. I am telling you this as a specialist in the field of computer repair. Of course, I was taught on pirated copies of DEC LSI-11, but the principles are the same as then and now. And in fact, if I were you, I would use boxes together with Tesla K20X 6 GB or K40 12 GB, and 2 Tesla K40 together would give you large crystal frequencies by 200-300 MHz and more by 200-300 CUDA cores, in K80 has reduced the number of cores and frequencies so that they heat up less. 2 K40 = 1 K80 +. And for the K80, I would buy a 3-unit box that you talked about and on the Asus server board that I mentioned - I assembled a system with 4 K80s. And I would have received not one, but several systems. Because of our fool-Putin who "is at war with all the world", when it is necessary to negotiate and trade, my income fell and I cannot afford to buy GPU cards and assemble a system with 4 K80 cards as I suggest you do. If you would give me a pair of K40s - or one K80s - I would be very grateful to you. Even the old K20M / K20X would help me. One K20X burned out, the fixing screw got on the contacts of the power controller and I did not notice it, and no one can repair them here.