Alright, so i checked out power consumption of my SOX 90w with BSX90 ballast. I am unsure of how the ballast exactly works, and how the internal windings are connected. Check out the picture of my ballast box.

Measured current with a non-true RMS multimeter is 540mA at 234v mains, so that indicates 126w.
With a plug-in wattmeter (Conrad EKM265, comparable to a Killawatt) it shows 109w.

If i can believe the wattmeter, the losses are fairly significant but still within an acceptable range.

thanks for providing the test results and technical information, @Laurens and @Medved and @RRK - very helpful in gauging the performance and efficiency of the Qianshun ballast.

so far, i am still VERY impressed with the 35W one i purchased.    i ran it for 12 hours yesterday and it was just barely warm to the touch afterwards. i also had a couple of voltage sags when my air conditioner started, enough to cause all my lamps to dim or flicker for a short amount of time, and the ballast re-struck the lamp instantly as expected, no "complaints" or issues.

i'll see how it holds up over time, and i have a Qianshun 18W SOX-E ballast arriving at my home tomorrow afternoon so i am looking forward to testing that one out as well.

assuming all is well with these ballasts over time, i will in the future consider a high recommendation of these ballasts to those of us looking for new, efficient gear to keep our SOX lamps running happily.

BTW - the magnetic ballast i have been comparing against is an Advance 71A0490 (photo attached). i have 5 of them and have been swapping between them for control purposes - all behave pretty much identically as they all have the same date code and were in more-or-less daily service at my workplace for the same amount of time (about 12 years). i've replaced the 14uF capacitors on 2 of them to bring them back within spec; the other 3 are doing fine. this ballast choice could explain why mine have higher losses - they're dual-purpose ballasts that can also run 55W lamps, so i imagine some compromises in efficiency were made to allow them to run both lamps.

Still I believe something is wrong with your magnetic ballast or meter. Ballast certainly lists 0.62A line current with 35W lamp on the nameplate, but you show 0.759A at close to nominal 123V on your watt-meter. PFC capacitor is bad? 

I also have the 35W QS ballast. However, the current is very low for a 35W lamp, about 320mA / 98V (measured with HF probe). You can also easily run the 18W lamp with the 35W ballast. The 18W lamp runs at effective 16W with this one. I don't have the 18W version, but I assume it's exactly the same.

Additional data point: my 18w SOX draws 29w at 240v using the same watt meter.
With a TRMS multimeter (different one than the conventional one at work!) the current is 154mA, indicating 37VA.
The efficiency of the SOX 18 is, in other words, quite bad. As far as i know this SOX fixture i have (The Philips Combi Pack thingie, forgot the model number) has a series choke style ballast.