Upgrading the Apple IIgs Power Supply

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bushnrvn's picture
Last seen: 10 months 3 weeks ago
Joined: Jan 15 2012 - 10:08
Posts: 193
Upgrading the Apple IIgs Power Supply

So this is an area where I lack significant knowledge.

I have an Apple IIgs with a Briel 4MB card, a CPM card, and a CFFA3000. I've preordered an Uthernet II and I've begun to wonder if I need to be worried about power usage. I sometimes run a printer, this isn't a must. I also hope to get an accelerator at some point...

I really don't have a good grasp on the power requirements of hardware from this era. I don't have the power supply in front of me at the moment, but I think it is ~100w?

Has anyone used the LittlePower\Pico combo as suggested by UltimateApple2.com?

Would I even need to consider upgrading power supply at this point?


speedyG's picture
Last seen: 5 years 1 month ago
Joined: Nov 16 2011 - 07:45
Posts: 2493
Re: Upgrading the Apple IIgs Power Supply

Hello bushnvrn,

well just some basic info:
Apple allways equipped their computers with rather "small" powersupplies....
( meaning that they serve with small average amount of load )

Powerusers that load up their computer often face 2 problems with their supplies:
they get hot and they "age" fast ( in sense of fast ageing capacitors etc. )
and the power gets instable resulting to dropouts and unpredictable crashes....

The regular supplies used at the II+ and IIe have limitation at 65 to 70 Watt
and that gets soon reached if using more than 2 external drives or
if adding external harddrive without own powersupply
same happens if the computer gets larger amount of memory added...

There are 2 rails you may think about:
If you want to keep your computer in original condition and don´t want to alter
the computer itself you may use a buggie-powersupply this was formerly made and sold by
stephen buggie ( you might google that by terms "buggie powersupply apple" ) or a similar
"external power solution"

If you don´t mind about alter of the computer you may modify the internal supply....
the solution you spotted out is one of several solutions....

You also may think about an "middle way" by keeping your original supply outside
of the computer on the shelf in a box and replacing while you use the computer by yourself
instead replacing a modded powersupply inside of the computer....

In such a case it´s recommended to get at least the case of a damaged similar powersupply
to use as case and thereby making sure that the spacings and measurements fit perfect as
"placebo" inside the computer while using it and keeping the option to switchback to the original
condition in case of sale by replacing the modded powersupply back by the one swapped out formerly
by the one from the shelf.

More important than the total amount of power in Watt is the specific powerlimitation at
the different voltages:
at regular power supplies from Apple the limits are with small differences:
+12 Volt : 1,5 to 2 Ampere
+ 5 Volt : 4,5 to 7 Ampere
- 5 Volt : 0,3 Ampere
- 12 Volt : 0,3 Ampere
the -5 Volt and - 12 Volt are only important at the Apple II+ or earlier computers because
there was common use of the 4116 RAM chips which mostly used that negative voltages and only very few
expansioncards use that minus voltages too...

So your eyemark is to focus at the positive voltages....
the +12 Volt is in general important for the limitation of external drives ( disk or harddisk )
and the + 5 Volt is important to the amount of the most used expansion cards and very many RAMcards
with huge amount of RAM chips....( many 4164, 41256 or also SIMM modules )
In such cases it´s recommended to have more than 7 Ampere availiable

another aspect is the potential amount of usage....
a powersupply with heavy load close to it´s limitation gets far more hot than a supply
that only is used at 60% of it´s limits.....
and it´s a question to think about how to get rid of the heat and get it away to outside of the case
of the computer.... that´s also one of the weak point´s of the computers from Apple....

Just for basic info´s about the powersupplies it might be usefull to visit my site:
you will see that there are several pages related to the topics of powersupply...
there is also a page that desplays with infos and pictures the mod of a Apple II powersupply
by "transplantation" of a PC-powersupply in a case of a Apple II powersupply and integration of
additional fan .....:
something similar can be done of course with he case of a IIGS powersupply case...


Last seen: 1 year 9 months ago
Joined: May 27 2013 - 13:01
Posts: 849
Re: Upgrading the Apple IIgs Power Supply

In my opinion, you can get yourself a "Bugg-Power" Buggie power supply, or you can get a MWP-302 power supply.

With the Buggie option, the power supply is external. It has the advantage of not producing heat inside the case and it will give you a LOT of wattage so you will never have to worry about not having enough power.

The disadvantage to the Buggie power supply is that modern power supplies do not contain the -5v rail that the Apple ii computers need so to compensate for this you would need to get the littlepower flip adapter from ultimateapple2.com: https://www.ultimateapple2.com/catalogzen154/index.php?main_page=product_info&cPath=1_6&products_id=8

That adapter is sold out at the moment but you can (if you know how) build your own:

The schematic to build your own can be found at this website:


If soldering circuits is not for you then the last option for a Buggie power supply is to get yourself an older ATX power supply that contains the -5v rail. The problems with this is that you will probably not be able to find a new one of these.

Now, the other option is buying the MWP-302 power supply. It is made by an independent company that was actually the builder and supplier for the "heavy duty power supply" that Applied Engineering used to sell. It is not an external power supply but it does have more wattage than a stock Apple ii power supply.

bushnrvn's picture
Last seen: 10 months 3 weeks ago
Joined: Jan 15 2012 - 10:08
Posts: 193
Closing the loop on this -

Closing the loop on this -


Finally picked up a power supply replacement this year.  Reactive Micro Universal PSU 1.3 installed and running. Glad to have tha peace of mind.

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