Power supply broken... but only the hard drive cable?

So, 2 days ago I got a new internal ssd to replace my old one (old one had very little storage space.) I opened up my PC, unplugged the power supply and sata port from my old ssd, and plugged them into the new one before putting the panels back on and trying to start it up. It was unusually quiet, and it took me far too long to realize that my hard drive wasn't starting up. At first I thought I had gotten a faulty hard drive, so I switched back to my old one. It didn't start either. I thought this was odd because I'd literally used it an hour before, so I tried the other two plugs on the cord for hard drives, for both the old and new solid state drives. Still nothing. Maybe it was the SATA cord? It was still fully plugged in, but I tried my other, slower one that's in my PC anyway and it still didn't work with either ssd, for any of the cords plugs. At this point I was really confused, because my power supply was clearly on: steady green light on my motherboard, case lights and fans on, graphics card fan on. I feel like it couldn't be anything apart from the power supply, but I'd never heard of a power supply breaking for only 1 cord, and couldn't find any similar stories when looking up the issue. The cord for the hard drives doesn't appear to be melted or twisted or anything. It's likely I've overlooked some other sort of issue, as I'm fairly new to tinkering w desktop hardware, but if any one of you have heard of this before it'd be a great help, so I can know whether or not it would be wise to buy a new power supply after I'm done triple-checking that I didn't overlook any stupid simple reason why it isn't working. Thanks! (btw power supply is a Seasonic, ss-850EM Active PFC F3, and the drives were an ADATA SP550 240gb (old) and a Samsung V-NAND 860 QVO 1tb (new).