Precision Power Supply

I have several M6X00 Precision workstations that use the PA-9E power supply. I also have a 7730 which came with a different PN/model power supply. I tried plugging the 7730 into one of the PA-9E supplies and it seems to work fine powering the laptop. I may purchase a 7740 in the near future with an i9-9980HK processor. Would it be OK to use the 7730 and/or 7740 with the PA-9E? And, if I bought a power supply specifically designated for the 7730/7740, would it be OK to use in on any of the M6X00 units?

 

Yes. The power supplies are cross-compatible. The newer ones are a little bit smaller footprint but otherwise functionally the same.

 

The old ones have a blue light on the plug and the new ones have a white light - very important consideration that

 

Btw, the dell sales rep was adamant an M6700 power supply couldn't be used on a 7740. Obviously desperate for that extra little bit of commission....

 

By voltage and dimension it has the same specs

19.5 VDC
7.4*5.0MM plug

Polarity is OD = negative ID= positive Center pin= resistor







The only thing that would make an older Dell charger not charge a new device is if they changed the resistor value on the center pin and added a whitelist into EC firmware blocking any charger not in this list and the EC is waiting for a response but only getting voltage but incorrect resistive value due to wrong resistor in your older charger.

This is what Lenovo is doing on their Thinkpad laptops starting with the **30 series.
For example T420s, W520, T520 or T420 etc was the last models that would charge using any 3'rd party charger and batteries, newer models won't charge if its not original parts so you must buy say a stock battery costing well over $100.
http://forum.notebookreview.com/threads/thinkpad-adapter-resistor-values.681124/
Just like they blocked the bios flash ability at the same time that would enable you to bypass the hardware whitelist list of FRU oem parts, you can reflash the bios but its required to clamp the chip and write to it via an eeprom by clamping the actual bios chip requiring complete teardown and removal of the motherboard.

Anyway you can't damage anything as the pinout has not changed.
Dell changing polarity would result in massive class action lawsuits against damage to customers properties due to fire or injuries etc etc.
Its either going to charge or its not, (see image below for polarity label)

 

I know the old ones work!

I'm just saying that the Dell guy said they wouldn't, presumably to secure sales of new ones...

 

Probably not so nefarious. He just doesn't know. it's a different part and it is safer to assume that the old one is not compatible, since it is not actually advertised as compatible anywhere. The reps' knowledge of these systems typically does not run very deep.

 

You are completely correct about "advertised", saying the wrong thing can have catastrophic consequences as you are representing Dell.
From time to time you do find a bright minded rep who know a lot and enjoy helping customers with technical questions.
But its better to keep to strict company policy even if you have
technological knowledge about the hardware and compatibility and whatnot unless you have a position where you can express your technological knowledge, not something a sales rep usually have training for unless you work in defense/military industry, which Dell actually do..they have the us gov on contract but I highly doubt they have other than a special rep team assigned for them with comprehensive insight into classified hardware customization and full disclosure and customization to source code for bios and firmware which you will never have a word with as a private end customer