Fear not, Internet denizens; Steam's brief failure was nothing sinister.
"Our data center's UPS experienced a power failure. Power is back on now and working to get service restored asap," Steam Support tweeted this morning.
Although viewers were directed to the Steam forums, no further information was given beyond a wry nod to the "uninterruptible" part of "UPS", and an apology.
Steam's web storefront, all clients, and Valve's own website were affected by the outage. Valve's staff identified and announced the problem in less than an hour following first acknowledgement of the issue, and services began returning shortly thereafter.