I recommend against this. Most supplies have a bleed circuit, but if it doesn't or it doesn't work (at all or not fast enough), then shorting primary-side capacitors can make a really nice bang and also damage your "shortening implement". That bang can startle you and make you hit something. Been there done both. Not a great idea IMHO.

Check for voltage - If not present / marginal, Then shorten, Else discharge through resistor and GoTo Check. A "capacitor discharge tool" automates this cycle.