I thought that ulracaps could be better than electrolytic ones for filtering after a bridge rectifier in a compact switching power supply due to their higher energy density. But, for some reason, I can't find any high-voltage supercapacitors on ebay or amazon. I could, of course, put a bunch of low-voltage ultracapacitors in series but that would defeat the whole purpose of a power supply being compact. Is there any reason why there are no high-voltage supercapacitors? There already are 5.5V ultracapacitors, which are basically two 2.75V caps in series, so why they can't go higher? Did I miss something? Are they hard to manufacture?