I'm trying to connect a pair of S5212F-ON VxRail TOR switches to a new pair of Cisco C9500-48Y4C-A using FS sfp28 DAC cables. I have a 5M Cisco/Dell custom programmed DAC that show serial and mac on both ends Line Up, Protocol down. Switched to a 2m Cisco/Cisco sfp28 and the link comes up. without issue. Ordered 3m because the 2M is a little short to manage and they won't come up. Clone the config from the 2m to the 3m still not working. Everything seems to be a problem on the Dell side as I can loop interfaced on the 9500's and the link will come up with everything except the Cisco/Dell custom programmed. If I program the Dell end of the 5m to Cisco it works fine in a loop. 

My question is there a power requirement on the SFP port to see a link? because currently it looks like the only real difference is the length of cable. Of course, I don't want to loop the Dell interfaces as that pair of switches is in productions. Any ideas?