There are a few ways an alternator can be too big.
If you find yourself having to change out the front springs to stop front end bottoming out after installing it, then its probably too big.
It could be too strong for the drive belt. Not likely a problem with serpentine, but a small V belt might have to be changed to a dual.
Its going to add load to the engine if you actually use the extra capacity. But, as long as you have more than 4 cylinders, doubtful you will notice.
The biggest danger is to the wiring. The wiring from the present alternator is sized for that alternator.
By the time you start drawing enough load to heat those wires, the alternator will have limited out.
But, if you slapped on a 400 amp alt and used 10 gauge wire to handle the output, then the possibility of smoke and/or fire is very real.
If you increase the size of that wire, remember all the wire further downstream must be increased, or have fuse protection appropriate to the size wire it is protecting.
Having the capability of large amounts of current, is no good if it cannot get to the need.
Everything should be fused correctly for the wire size now, with the possible exception of the output wire from the alternator.
Replacing that one should not cause problems.
However trying to draw more current than you can now on other circuits will result in blown fuses unless you upgrade both the fuses and the supply wire for that circuit.
