For a Dell Latitude E6440, I can absolutely confirm that the 60-65 Watt power supply will cause the CPU to throttle down. Been having the mysterious slow-down when plugged in since I got the laptop. Shifted power management to high performance for every configuration. Resulted in the computer being blazingly fast when running on battery; slow, glitchy, laggy, and a pain to use when plugged in. Was told by employer ITS that they would re-image the machine and then, if the problem continued, check the Power Management software. So, in advance, I upgraded the power management software. Lo and behold, when the adapter was plugged in I started getting the "below 90 Watts" warning. that warning had been disabled (and not by me) before I was issued the machine. Adapter issued was a 60-65 Watt one. Found an old Dell power supply that ran at 90 Watts, plugged it in, and - Shazaam! - problems disappeared. Got hold of monitoring utility for the CPU and a benchmarking utility to stress the CPU. With the 90 Watt Dell adapter, with load stress, and with 20+ tabs (including 4-5 streaming video), audio, and two applications open, the CPU clocked at 3.1 GHz and never lagged. With the 60-65 Watt OEM adapter, it clocked at 0.80 GHz and glitched per usual. Couldn't even charge the battery more than 2-3% over an hour with the other stuff going on.
I use my computer about 6 to 8 hours a day, on average. The glitching and lag has cost me 5-10% lost time in waiting, and rework, not to mention frustration and time spent trying to solve the problem. Or, about 4 to 6 weeks of unproductive time. Various blogs have blamed it on the WiFi channel, the Power Saver settings, some mysterious configuration of the motherboard... Turns out, its a deliberate configuration on the part of Dell.
Nice... Great way to build a rep.