Although this laptop is older (2012), it is still very functional, fast, and I use it for everything (even though I just bought a newer XPS 15, 9560). For awhile now, it has the problem where the power just randomly cuts out if it is off the power adapter for more than a few minutes.
It's not the battery. I had the original battery tested, and it was fine. I even replaced it with a newer battery (also tested and in excellent condition). It's also not the adapter, which works fine. I even bought a new one of those, which also works fine, despite a loose connection at the power-in side.
What could cause this drop out? According to the battery guide I should a) have at least 3-5 hours of power when disconnected from the adapter, and b) get some kind of battery low warning before it shuts down... and it does not shut down or sleep... it just dies, as if the battery was removed completely and the power plug pulled unceremoniously.
While I'm asking questions, where can I get a replacement AC cord for my adapter? The one with the three-prong plug on the adapter end.
"loose connection at the power-in side"
Sounds like it is shorting out the system. Disassemble the laptop to reveal the RMD72 DC-in cable.
Be sure that the screw holding it affixed is secure. Re-seat the other end onto the motherboard. Dell is not going to have parts for this 2011 model. You will need to search on the web for a reseller for power cord part 199XY 240v or K055K, YJ782 250v.