#2. Just one scenario I came up with.... Let's presume that the battery can either be discharging or charging, but not both simultaneously. That makes sense, right? So, maybe you can power the W520 from 65W/90W most of the time, but occasionally something kicks in and the current draw spikes. Suddenly it has to switch from AC power to battery power. Okay, fine let it. But let's say you have different settings in the power manager for AC/battery screen brightness -- as it does by default. Maybe also for WiFi power. USB standby. GPU settings. And maybe the threshold is crossed every couple of seconds (even several times a second).
I could see a situation where a computer was reduced to a beeping, flickering hysterical mess by trying to switch back and forth too often. Yeah, you could "fix" this with a custom power scheme, but the out-of-the-box experience on an Energy-Star-labeled machine could be pretty nasty. (I wonder how the Mac PowerBooks with their 85W power supplies handle this. MikeM, you still here?)
I think there's an similarity to uninterruptible power supplies
. Most are "standby" systems where only one power source (battery+inverter or line) is connected to the load. A more expensive "online" (or "double-conversion") always has the load connected to the battery+inverter and available line power can run the inverter and/or charge the battery as appropriate.
If this idea is remotely connected to reality, then perhaps what we need is for Lenovo to come up with a power handling circuit more like the online UPS... but responding to load rather than line.
#1. Could it have anything to do with whatever mechanism is used to sense the current rating of the power supply being incompatible with older machines? I really have no idea. Indeed, it seems like what they needed to do was prevent connecting a too-small adapter, but the plug redesign does not achieve this. But if they really wanted to gouge on adapters, they'd follow Apple's example. (How many different video ports have they come up with over the years? Round serial ports, too.)
W520 (2820QM, Q2000M, FHD, mSATA SSD, dock)Previous: T61p (died 1m past warranty ), Dell 8600, iBook ("Dual USB"), Gateway Millennium, Macintosh G4 , PowerPC Mac clone, Mac Duo 210, iBook (clamshell), Quadra 630, Mac IIsi, C-128, C-64, Vic-20