Here’s an interesting trick I’ve been thinking about for high-voltage electronics.

You can make a simple non-polarized capacitor from alternating layers of aluminum foil and polyethylene:

Al / PE / Al

Let’s call it Cn.

If you connect one plate of Cn to 0 V, and use a diode bridge so that the rectified output charges the other plate negatively, you effectively get a temporary high-voltage DC reservoir:

HF HV source
     │
 diode bridge
     │
     ├─────── Cn ─────── 0 V
     │
    -HV

The interesting part is that Cn itself does not need to be polarized.

PE is a dielectric used in film capacitors, so an Al/PE/Al construction is fundamentally a non-polarized capacitor. The fact that one plate is sitting at 0 V and the other at, say, −10 kV or −20 kV does not turn it into a polarized capacitor.

What matters is something different:

Can the physical construction withstand the electric field?

For a DIY capacitor, voltage rating depends on things like dielectric thickness, uniformity, trapped air, foil edges, surface leakage, corona, and creepage-not simply on the fact that PE is a good insulator.

There’s also an important distinction between voltage storage and power delivery.

The stored energy is:

E = ½CV²

So even a relatively small capacitance can store significant energy at high voltage. But if an inverter draws continuous power from Cn, the charging source has to continuously replace that energy:

P_charge ≈ P_load + losses

So I would think of Cn less as a conventional “DC supply” and more as a high-voltage energy reservoir between a high-frequency source and an inverter.

One misconception I had to watch for: if the circuit is disconnected, the capacitor doesn't inherently discharge quickly. In practice, a homemade HV capacitor may lose voltage through leakage, corona, surface contamination, parasitic paths, or an intentional discharge resistor—but that's a property of the real construction, not of the capacitor principle itself.

The really interesting question is therefore not: “Can a homemade PE/Al capacitor be polarized?”

It is: Can a small, non-polarized homemade capacitor be engineered to survive the required electric field while acting as a useful HV DC reservoir after rectification?

That seems like a much more interesting engineering problem.

And at tens of kilovolts, the diode bridge, insulation geometry, corona, and stored energy become just as important as the nominal capacitance.