Simples, increase DMG by 50% per stack debuff so at 4 stacks, it's 200%. If 5 stacks, total 250% DMG increase. That 250% DMG increase along with 62.5% increased DMG from 5 stack debuff. The 5 stacks is only possible with 1+ Shock effect Max.
I think Hirling Stack Debuff can count into electrocution to fully maximise it.
That's basically total increased DMG= Over 400% increased DMG by shock alone. That electrocution is extremely good.