Just got the new AC Adapter - PA10 - and the laptop works fine. I had to rollback the system restore to get the WiFi to work but everything else seems normal. The PA10 does charge the battery faster than the PA12 also.
So... if things are acting wierd with your Dell's power situation, try a new GENUINE DELL adapter, not a knockoff you find on eBay.
I had the same issue with a Dell studio XPS 13 the rep sent out new battery and AC adapter, seemed to fix the issue.
But getting Dell to enter the defective returns correctly into their system...thats a whole different story...