As ever, a full circuit diagram would be invaluable - even if to show that there is nothing much more present than has been stated.
VAC = 220V so Vpeak = 220*1.414 =~ 310V.
180V DC/310 =~ 0.58
This is the sine of thge angle when the rectifiers start (or end ) conducting + 35 degrees.
For 35/90 of the cycle the voltage in is below Vdc so the cap MUST provide the motor current. If you do not have any energy storage in inductors then the cap is seeing a ripple current of in the order of the motor current and peak currents will very likely be higher (depending on transformer and wiring resistsance and more.)
As dissipation will be in the order of proportional to current squared you probably have about 10 x rated dissiation due to excess ripple current.
Nichicon are a well respected brand. Chances are the actual ripple current capacity on a genuine Nichicon meets or exceeds specifications. But it is unlikely to exceed it by enough to save you here IF the circuit is as it seems. It is possible that the cap is a counterfeit. This definitely happens and Nichicon are a well enough known brand that people MAY counterfeit them, although I have no specific knowledge of this happening in this case.
UUCAP I know not.
It is not unusual for little known Asian components to not come close to spec sheet claims.
In this case it appears that they exceed the specs handsomely !!!!
I'd not complain!
But do look at the actual ripple current.
A small sense resistor in the cap ground lead will allow a scope to be used with due care (or in the "hot" side with an isolation device AND if you know what you are doing. Or a Hall clamp / proximity meter or ... .
Note that cap lifetime ~+ Rated hours x 2 ^ [(Trated-Trun) / 10 ]
It is usual to run a cap at WELL below rated temperature.
30C below = 2 ^ (30/10) = 8 x rated lifetime.
So a 2000 hour rated cap would last about 2000 x 8 = 16000 hours ~= 2 years.
The larger margin the better.
Note that an Al electrolytic cap with NO applied voltage, held at high temperature will die faster than when voltage is applied !
Electrolytic capacitors do have a mechanism whereby some DC measurements show different values. Once you are in the audio band, it's likely to be constant from 20Hz to 20kHz.
The question is, what method does your Fluke use to measure their capacitance? Does it apply 1kHz AC, in which case the measurement will be true for the audio band as well. Or does it apply a DC current, and measure how quickly the voltage changes over a period of seconds? This latter method is prone to errors from leakage current (big anyway with electrolytics, especially horrible with new ones), and from charge absorption (have you ever watched the voltage reading on a big electrolytic that's been charged and quickly discharged grow again, over the course of minutes?)
As the DC leakage depends on the charge history of the capacitor, there's no reason that similar DC measurements should correlate to similar AC measurements. So it's important to find out what measurement your meter is making.
Why 10% and 20% tolerance caps? The purpose in life for an electrolytic is storing energy in power supplies, not much else. They don't need a good tolerance, so they're not built to a good tolerance. The form of construction doesn't lend itself to good reproducible dimensions anyway. But with automated assembly on high quality machines, it's not surprising to find several capacitors made in the same batch to match to within percent.
Best Answer
An interpolation (or worse an extrapolation) is only as good as the data points you have, and your reasonable expectation about the order of the function between (or worse outside) those points.
If you don't know the function, there's little point doing an interpolation.
If you have one point from the datasheet, then a zeroth order (same constant value) is a reasonable guess until you've measured the ESR at several frequencies to characterise the function.
If you have two points, then many people would be happy with a straight line drawn between the two. However, some might prefer a straight line against log frequency, and the more cautious would worry about whether there was a resonance or knee somewhere between them. Until you've measured the ESR at several frequencies to characterise the function, you won't know.