I've got an old gaming laptop which comes with a very annoyingly big brick PSU, rated at 100W and 20V. I do not care that the PSU is heavy, but it has a weird form factor, and I always have to drag it around. Looked around, and did not find any slim power units (besides, not including the PSU weight in the laptop weight spec is cheating, imho).

So I wonder if I can get four of these, seemingly high-quality, low profile PSUs, each rated at 5V and 5A (25W each), bolt them onto the laptop on the side, and wire them together to get 20V and 100W. Also, these are modular, so once the laptop dies (this thing just wouldn't die!) I would have many other uses for the PSUs. I am not quite sure how to route the AC to them -- split the cable into 4 in parallel?

There was a topic on combining DC power supplies, but I wonder if, for a laptop, I need special precautions.

Thanks in advance!


  • \$\begingroup\$ Such modules are intended to be installed inside an enclosure that shields the user from coming into contact with the PSU. The terminals in particular are quite exposed on such PSUs. Just FYI. \$\endgroup\$
    – marcelm
    Sep 10, 2017 at 16:14
  • \$\begingroup\$ What is weird in the formfactor of your original PSU? \$\endgroup\$ Sep 10, 2017 at 16:46
  • \$\begingroup\$ maplin.co.uk/c/computing-gaming/laptop-accessories/… \$\endgroup\$ Sep 10, 2017 at 16:59
  • \$\begingroup\$ Yeah, the top one on the list is the size my is. \$\endgroup\$ Sep 10, 2017 at 19:53

2 Answers 2


Current sharing SMPS is ripe for instability with 4 feedback loops sharing the same output. It is unlikely to be smaller than single SMPs as there are redundant packaging and primary side functions.

Look for a better universal Laptop charger and you can reduce power needed by dimming the display and not using when recharging by 50% or expecting a slower charge time.

  • \$\begingroup\$ I think the point on 4 feedback loops sharing the same output is important, so I probably should not be doing this. Otherwise, the open design of the 'baby' PSU would allow me to run a a fan and cool is better. The current brick is a plastic brick with no air flow at all (just like all of them) \$\endgroup\$ Sep 10, 2017 at 19:55
  • \$\begingroup\$ Dont get a smaller PSU, I just read it runs slower if insufficient power. but this looks ok amazon.ca/Lenovo-ThinkPad-W510-4319-65U-Adapter/dp/B00UHDIEKS/… \$\endgroup\$ Sep 10, 2017 at 20:17
  • \$\begingroup\$ I concur, a smaller 100W PSU (an IBM-branded one) indeed slowed this machine down. \$\endgroup\$ Sep 11, 2017 at 15:42

Smaller PSUs (and with smaller voltage output) are usually less efficient than PSUs with higher voltage output. Just consider the voltage drop in secondary rectifier relative to output: with 5V/5A the rectifier drop of 1V is 20% loss, while 1V at 20V output is is only 5% loss. Stability concerns aside, four "baby" supplies in series won't be any smaller than a single 20-V supply. Also using open frame designs in portable electronics is really a bad idea.

More, you didn't mention what brand your laptop is, or if the power connector has a third pin. Many laptops have several kinds of identification, allowing laptops to scale their power consumption (and charging) to align with PSU capability.

  • \$\begingroup\$ The laptop is the IBM W510 which was top of the line 7 years ago, so it's quite power-hungry. All PSUs are plastic-enclosed bricks, so I presume they have to be big to dissipate the heat better. So I was hoping that a more open design with a fan could be made much smaller, or at least less awkard shape. \$\endgroup\$ Sep 10, 2017 at 19:57

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