he most compelling issue is why my 18W pump is running on 14-15W?
The pump has a absolute maximum power consumption of 18W.
When you power up the pump the power consumption is for a short time more than 50W.
The power consumption is also depend on the resistance in your water loop and some other individual parameters.
That would make perfect sense; unfortunately, RPM of pump connected to poweradjust is lower than connected directly to molex (~4550 vs ~4750). Which actually translates to lower cpu's core temperatures (up to 3'C, which is surprisingly high difference). As I was very content with aquaero 5, this poweradjust thing is imho just overpriced piece of junk

Well, maybe "junk" is too much said; but it certainly is not worth 50 bucks.