If you hook up 12VAC to a rectifier, you get about 17v P/P slamming into those diodes. Try it with one putting out 9 VAC
Also be sure it is really hooked up right.
On the square bridge. AC is East and West, DC is North and South. (Look for the plus sign to get oriented)
Of course that assumes these are just diodes with a resistor. If they have a smarter PS, who knows what will happen with unfiltered DC.
It may give you the effect of the whole 17v
