? Two capacitors in parallel results in double the capacitance of one.
The two capacitors are meant to be in parallel; they are C121 and C122:
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On the horrible daughter board with SMD capacitors, those are in some sort of series-parallel arrangement, but the reliability of those is so low that they should be replaced on sight with two "M&M" capacitors (preferably 3 kV voltage rated types, minimum 2 kV).
My guess for why they blow so frequently is the pair of inductors just past them. Something interrupts the current flow quickly (e.g. the 20 A fuse in the motor controller blows), and the energy from those two inductors goes mostly to those two capacitors. The instantaneous voltage could well be in the kilovolt range. Thinking about this, it's a good thing that these relatively cheap and accessible parts die, saving the way more expensive and near impossible to replace IGBTs and diodes.