An excerpt from the aforementioned answer:
The flight units used by mission, with power levels at launch, were:
Galileo: Flight Units 1 (289 We) and 4 (288 We)
Ulysses: Flight Unit 3 (289 We)
Cassini: Flight Units 2 (296 We), 6 (294 We) and 7 (298 We)
New Horizons: Flight Unit 8 (245.7 We at bus instead of connector pins)
The listed power levels are electrical power levels in watts (We),
So Cassini (1997) had 1.5x the power budget of Galileo (1989), 3x that of Ulysses(1990), and a bit over 3x that of New Horizons (2006).
What made it have such a high power budget? Or did it have a similar power budget to other probes, and just was unable to use solar panels? I see here that NASA decided that they couldn't use solar panels, but it doesn't appear that the other missions use solar panels either. And it also doesn't seem like it's a matter of age, since there were much smaller power budgets for probes that came both before and after.