What would be a good choice for a graphics card for a HP DC7900 Windows 10 64bit because of the low power supply?

Here is the specs.....

https://h10057.www1.hp.com/ecomcat/hpcatalog/specs/provisioner/05/KP721AV.htm

Any help you can provide would be greatly appreciated.

You didn't reveal what this graphics card is for or what monitor it would be driving.

However I will share my power consumption tests on an old HP dv9000t with the Core2Quad CPU and what it peaked out at with a few cards.
I had tests with the GT 240, 1050 Ti and a 1060.

Numbers are over at https://www.cnet.com/forums/discussions/im-upgrading-some-old-iron-what-would-you-like/

  1. GT 240 was Max: 1.32A or 160W max during tests.
    Idle: .69A or 83W.
  2. The SSD helped too and was Max: 1.15A or 140W max during tests.
    Idle: .58A or 70W.
  3. 1050 Ti was Max: 1.43A or 173W max during tests.
    Idle: .58A or 70W.
  4. GTX 1060 6GB came in at Max:2.07A or 250W max during tests.
    Idle: .60A or 72.6W

All the models noted an 85 plus PSU at 240 Watts so at 85% efficiency your PC's limit would be the GTX 1050 Ti 4GB in some low profile model.
Many will pull back to the 1030 but that would not be suitable for say someone that is trying to game as 1080p 60Hz today.