Looking at the SDS of the non-aerosol version of the CRC stuff vs. the Purple Power there's quite a bit of a difference. PP has 25% lye(Sodium Hydroxide) which explains why it corroded your aluminum. pH seems to be same but I would trust the CRC stuff. I've been using Simple Green HD(purple liquid) or WD-40 Specialist Water-Based Degreaser for my underhood cleaning. They aren't as caustic to Al as Purple Power/Super Clean and its clones.
I don't think the PP contains 25% NaOH. It contains 3-4% of a 25% NaOH solution or 0.75-1.0%. It is probably used to adjust pH for solubility and clarity which is a common practice is water based cleaner/degreasers.