I can tell you for certain, I measured my plug phiips (foil and 'one') and they are both 14VDC. So short answer is that the plug charger would blow up the usb trimmer you have (which is 5VDC).
The reason I know this and measured them, was because I wasnt sure the two plug chargers were the same, and I didnt want to blow up my philips one.
For now, yes. You actually believe that will continue to be that way in 12 - 18 months?