Kelvin waterdrop electrostatic generator
The problem with earlier electromagnetic electricity is that the culture goes modern very quickly as people keep taking the next step. But if you use an electrostatic generator there is no next step.
Kelvin's water drop generator uses drops of water falling through two sets of two loops attached by wires in the form of an x, so as the top loops connect to the bottom loops opposite. The droplet falls through the top positive loop, falls through the bottom negative loop, and vice versa.
The advantage is that this allows both spark nitrate formation for nitrate explosives and fertilizer. You can use electrolysis for perchlorates for bleaching, peroxides for paper delignification, persulfates for phosphate fertilizers. You can do electrorefining for decent metal alloys and steels, and even electrochemical machining for decent steam engines, all without magnetic fields, and all using watermills millponds that are free when you aren't grinding grain.
You get a Roman empire that is stable against technological advance, and that has cannon, gunpowder, spring from alloy steels for decent recurve bows, plows, saw, nails, bearings, steam engines, more gold and silver for currency, etc. Lots of alternate history potential.
You can also build decent sailing ships that can go around the world with a cargo and a desalination rig. Roman legions vs American natives, not to mention China and India.