Finally got around to checking everything out today. Multimeter showed a good 11.5 VDC at the outlet. Never thought to check my inline 10A fuse since I had good power, but I pulled it anyway. Never saw this before: the fuse had blown, but the pieces of metal visable through the fuse were still laying close enough to allow arcing. Multimeter on the fuse was alternating between an open and .5 ohms rapidly. Changed the fuse and voila, everything's fine again.
Should have checked the simple things first! Thanks for your suggestions.