Just FYI:
In some cases, contractors running a national park have installed electric pedestals, and when it does that, it charges a higher fee. It still allows discounts for Camp Sites, but then adds a non-discount fee for electric.
As I recall it in Teton NP, the camp fee was $26, and we paid $13, but the power fee of an extra $11 made the site $24 w/electric. It would have been $36 with no discount ... so the numbers don't add up exactly, but this is close. It was a couple years ago and I don't have receipts - and memory does what it does without our help :) Not all sites have electric upgrade.
But it shows that contractors in a park do add fees for services in come cases, and still honor the discount for Senior and Disabled pass for campsite, but not extra "services". We chose to stay in a non-electric site - so we paid the $13 per night.
