While I've never personally gone looking for the outlets, I've been told that they are at 19 and 55. I've also heard reports that from time to time the outlets are partially, if not fully blocked by the seats themselves. This could be especially true if you are planning to plug in a brick. So you may want to bring along a surge protector or at least a short extension cord.
Failing getting a seat next to an outlet, you should be able to recharge things in the cafe car at the outlets by the tables on the lower level. There is also an outlet in the upstairs service area, but I would ask for permission before trying to use that outlet. Some crews don't like people behind those counters, even though they aren't used except on the Empire Builder.