I not only answered my own question, but it appears I answered it incorrectly.
According to a source on the Yahoo message board for Delta, the 737-800 does have the EmPower system. It is a single hole located below the seat cushion level.?? In other words, you have to bend way over to find it.
It's at every seat in first, and 3 seats share a jack in coach.
They probably don't have the cords on board since the F/A I asked about it said it didn't even exist.
Someone let me know if you find the input jack and can get it to work. You will probably have to ask for the system to be turned on. Go figure.