Assuming your machine is a dell optiplex or similar and that pau is one of dells proprietary units with an 8 pin motherboard connector you'll get away with a bus powered 750ti fine
A PSU upgrade is out of the question anyway , these units only supply 12v current & the 3.3/5v split is done by the board.
The bonus of this (if you can call it that) is that you have 260-270 12v wattage available for what is realistically only a 200w system even with a 750ti installed.