If your PC's came configured that way from Dell, they're fine and all is covered under warranty.  The RX 550 is only a 50w card. Spec sheet for the Optiplex 5070 can be Googled.  Not linking it since I couldn't currently source it from the Dell site. As configured from Dell, the 5070 SFF comes with 200w PSU.  If in doubt, you can always double-check yours.  It's the MT that comes with 260w PSU.  360w PSU redxps630 described as "Dell oem" comes from another model that also works for the 5070. The RX 550 is one of the graphics options mentioned on the spec sheet.  Screengrabs below, 3rd one showing PSU's.  (90w PSU is for the micro.) [IMAGE] [IMAGE] [IMAGE] As for 400w PSU for a 50w card, that I don't know where it came from. Aftermarket PSU's can be a different story than Dell PSU's.  A PSU has various rails, or lines of power.  Aftermarket PSU's often have less power on the 3.3v/5v rails than Dell, but boast more total power.  So, a 400w aftermarket PSU might have more power on the 12v rails than a 305w Dell PSU, but still less on the 3.3v/5v rails than the Dell.  GPU makers will always suggest/recommend a PSU wattage based on covering the bases in regards to aftermarket PSU's and possible PC configurations. So, as long as your PC's came configured from Dell with RX 550's, then you can be confident the Dell PSU can power it and your PC.  If the person that ordered the PC's also ordered the GPU's separate, and let's say the GPU's aren't on the spec sheet (or other Dell documentation), and/or wattages not within Dell specs, then we could be looking at something else. Hopefully I eased up any confusion.  That's fine if you still have questions. It's also good that you questioned the GPU's.  Older Dell specs did require higher wattages for certain GPU wattages.
I am wondering what the highest possible PSU for this computer is. I have 30 of these machines in a lab and someone purchased, without my knowledge, 30 graphic cards that require a 400-watt PSU.
OptiPlex 5070 SFF and upgrading PSU