The first thing I would be careful about is make sure that the replacement fans offer adequate CFM. While the Dell fans (Foxcon) are noisy, they move a lot of air. I believe they are rated around 150 CFM. A quiet fan is going to be a lot less than that. But there are some relatively quiet high output fans on the market, just avoid the mistake I made, avoid the super quiet 1000 RPM fans. They just won't push enough air.
I am told that replacement fans might also run into a F1 boot error... apparantly some fans do and some fans don't. I am not sure which do and which don't. I am running my Dell headless, so this was a big deal for me (no keyboard attached to hit F1).
You can run a fan that uses less than 0.9 amp, but I would not exceed that value. I would avoid fans, like some Delta fans, that pull 3 amps. They are way to amp humgry. Most fans should be okay though, for example, the new Noctua 3000 RPM fan pulls less than 1 amp.