Should be fine and notice this page which shows the adapter is compatible with thee 3020 and the 7040. I assume you have that same adapter.
I had an OptiPlex 3020 that I upgraded the PSU so I could use a better GPU, and to do so was using a 24 to 8-pin adapter into the motherboard. After a year of success the 3020 has died and I've bought a used 7040 to replace it. It looks like I should be able to use the same adapter on the 7040 as I did on the 3020...? Anybody know for sure?
7040 power adapter the same as for 3020?