I thought I'd set this thread up as something we could list in the UA FAQs, especially since I'm an Empower whore and am constantly seeking answers.
If you have anything to add to this thread, PM me and I'll make the update.
Necessary Equipment
EmPower is a 15V DC (up to 75 Watts) system that can power (and possibly charge) your laptop and other electronic devices. The outlet looks like
this, so it requires a special power supply that works with DC as well as a plug that works in the EmPower outlet. Note that with the thin connector pins, all of these plugs are somewhat fragile...so be gentle when plugging & unplugging them. A few years ago I broke a pin at the beginning of a SFO-HKG flight...didn't make for a very enjoyable trip.
My preference is the
Igo Juice product since one "brick" can be used for both AC and DC uses. Plus it has a nice blue light on it...makes a perfect hotel room nightlight.
There are tons of adaptors available, but the important thing is that it has a connector that will work with the EmPower outlet. Almost all products indicate on the packaging if they're compatible with EmPower as well as your PC model.
Note that there are adaptors for the EmPower plug to a cigarette lighter-style plug. Some airlines, including AA, use a cigarette lighter outlet instead of the traditional EmPower one. These adaptors allow you to use the same DC power supply despite there being different plug configurations.
Also, keep in mind that with these "generic" power supplies, there are some PC manufacturers out there (especially Dell) who design their products so only Dell-labeled power supplies will work. Definitely something to consider before dropping $100+ on a DC supply.
Availability
EmPower is available in United First Suite on 744s and 777s, United First on domestic 777s, United First on 767s (both domestic and int'l configs), United First on domestic* 757s, United First, Business, and Economy on p.s. 757s, United First on A320s*, and United Business on int'l 744s, 777s, and 767s.
A note about 757 p.s. and new Business and First Class Equipment - the laptop power system on these aircraft accept traditional AC power supplies & wall plugs. Essentially, you only need to bring the power supply that came with your PC and no "special" adaptors are needed, at least if you're using the standard North American plug configuration. I can't speak to adaptability for European, Asian, and other plug configurations, but if you use a North American adaptor it should work just fine.
Circuit Breaker Locations
The EmPower system has a main on/off circuit breaker. You can tell if the system is on because each outlet has a green indicator light. It's been my experience that most FAs are not very savvy in knowing where the master EmPower switch is, so it's worth your while to check here so you can perhaps guide the FA should that be necessary.
In general, I find that the plane's first flight of the day will usually have the system off when I board; my guess is that maintenance turns it off when the plane sits overnight.
B744s - I believe this control is located in the actual cockpit, although I cannot confirm. About 4 years ago I was flying NRT-SFO, and the UD FA called the captain and the green light came on.
B777s (International) - Not sure.
B777s (Domestic) - Not sure.
B763s (International) - Located in the entertainment cabinet in the F galley area, at the front of the right (starboard) aisle. At the bottom of the cabinet, below all of the movie tape decks, on the right side of the cabinet, there is a little box that says "Power Module" with a switch on it.
B763s (Domestic) - Not sure.
B757s (p.s.) - Not sure.
B757s (2-class) - Not sure.
A320s - In the entertainment cabinet that's in front of 1AB, the door opens upward horizontally, and at the bottom of the cabinet there's a switch. Note that this cabinet/bin is essentially above eye level, so it may require standing on tippy toes to see the switch.
*The Annoying EmPower Situation w/ non-p.s. 757s and A320s
While we're grateful that some 757s and 320s have EmPower, there's a good amount of them flying around that have a nasty little plastic cover over where the EmPower outlet should be. It's a total crapshoot as to whether your 757 or 320 will have EmPower, and it's quite annoying, frankly. Even though there's no way to find out the specific equipment that will be operating your flight beforehand, I have kept a log of 757s and 320s that have and don't have EmPower.
There's a suggestion that the Overwater 757s (those that go to HI) do not have the system, although earlier this week I was on an OW 757 and the EmPower was there. That said, the few '57s I've taken to HI have NOT had EmPower, but the reason I've only taken a *few* is because I prefer the 767s and 777s that reliably have power.
757s & 320s WITH Empower
757s:
N503UA
N504UA
N506UA
N507UA
N511UA
N513UA
N514UA
N515UA
N516UA
N519UA
N520UA
N528UA
N530UA
N531UA
N534UA
N537UA
N542UA
N543UA
N549UA
N550UA
N558UA
N577UA
N579UA
N583UA
N587UA
N588UA
A320s:
N419UA
N421UA
N422UA
N423UA
N424UA
N426UA
N427UA
N429UA
N431UA
N433UA
N443UA
N462UA
N464UA
N466UA
757s & 320s WITHOUT Empower
757s:
N501UA
N521UA
N523UA
N524UA
N527UA
N529UA
N540UA
N541UA
N546UA
N551UA
N559UA
N561UA
N562UA
N564UA
N566UA
N567UA
N569UA
N572UA
N575UA
N576UA
N578UA
N583UA
N585UA
N589UA
N593UA
N596UA
N598UA
A320s:
N401UA
N403UA
N404UA
N409UA
N413UA
N439UA
N477UA
NOTE: You can also rest assured that if your A320 has a row 27 (likely a reconfigured ex-Ted with 6 extra seats than the first generation A320s, there won't be any Empower since UA made one of the most ridiculous business decisions to retrofit without installing laptop power).