I have the SP GT2 Pro and replaced the monstrous capacitor with one bought in a regular electrics store for about 1£. If you put a SP sticker on it you can sell it for 10£
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The specs on mine are 25V and 2200μF and works fine. But I guess the 25V is unnecessary since the esc doesn't charge it that much anyway.
Maybe someone with more knowledge in electrics can tell the minimum specs in V and μF you need. Smaller values means smaller size of cap.