Power over Fiber? None.
But Fibers are mostly always up unless and until their source OLT goes down as they can mostly travel long distance without any booster.
For other mediums though, it gets tricky. There aren't a lot of ISPs anymore that use Coaxial or DSL but there are some who use FTTC with Act Fibernet being the major player here. Their distribution boxes have battery backup but it can last only for few hours I guess.
Best case scenario is getting your own power backup with any FTTH connetion.