just lost power for a split second, which caused the PC to reboot ...

Are there power supplies which enable a PC to withstand such a brief power hit? I normally build my PC from parts and I don't skimp on the power supply. Yet, I have never noticed any being sold with a built in UPS or advertised with the ability to maintain power for a few seconds.

I have a small IBM AS400 server running sometimes. And more often than not when I lose power like this the AS400 stays up while the PC falls flat.