Isolating bridge rectifiers through electrolytic caps...

I need to use two bridges on one transformer output. one bridge will supply differential rails and the other will supply a single rail that is higher than the differential rail. I need to isolate the other bridge but I don't know how to judge what value or rating the caps need to be. is there a rule of thumb or actual equation for this? Can I use this method on a circuit that will consume substantial current +500ma?

why need isolate?

bridges provide some isolation

I start to pull a load through the secondary bridge when hooked up without the isolating caps. same reason why the SSLtech PSU is done like that.

??