studioman22 :
Yeah well speaking of holdup time, I don't understand why these PS manufacturers haven't included basic power loss protection for like 2 to 3 seconds. A very brief power outage is what happens most of the time, and then the power comes right back- but it's often enough to shut the system down. Instead we have to buy an expensive online UPS. There has to be a way to do this on board the PS, even if the PS costs more.
The answer is simple... have a look at the insides of the Seasonic X-650:
See those round things, white with a blue band, and those small round brown? They're called capacitors... to be able to keep the voltages stable and steady for even a second at 650w, these capacitors would probably have to be as big as those two capacitors on the input side - there's simply no room in the power supply for such big capacitors and even if you'd somehow make them sit over some integrated circuits, the air circulation inside the case would be horrible, components would heat and so on.
You could replace them with ultracapacitors which MAY be able to provide a few seconds of time in about the same diameter (but they'd be higher) but at about 3-5$ a piece versus 10-30 us cents for these regular capacitors, you're basically going to double the cost of the power supply.
Besides, I'll have to disagree with you. Where I live, there's power failures about 3-4 times a year... maybe once for less than 10 seconds and the other 2-3 times for about 10-15 minutes and the whole neighborhood is offline.
To power a computer these power supplies are designed for (about 300-400w constant usage when playing games) an
average UPS that costs about 90$ has a battery that weighs about 6 Kg, it can keep the system running for 4 minutes and then needs to recharge the battery for 16 hours until it can keep up the system running again at that power usage level.
Even if you'd make a UPS that would hold the power for 20-30 seconds it would still be about 2 Kg, it would be just as big as a power supply, it would need about 5 hours to recharge after a power loss (during which it would be useless), those 2kg extra would probably increase the shipping price of the psu by about 15-20$, and so on and so forth...