[chrismcb]

Why is tx and px better than pro and pro Max? Typically pro Max is going to offer you more or better than what pro does. So pro Max tells me that it is probably better than pro (without designing what "better"is) but TX and PX which one is "better" and you can't always go by the price.

[dagw]

In this particular case TX and PX are referring to PSUs complying with certain third party certifications, and have a specific quantifiable meaning. So in this case Tx is always "better" (or at least not worse) than Px in a very specific sense.