I’ve just bought a secondhand QC and as well as the original power source, it had a back-up power supply (see photo). Is this suitable for the QC? Also does anyone know if there’s a means of locking or fastening in the power connector as I’m worried that it would be easy to accidentally pull out on stage. Thanks. S
Electrical engineer here.
12V 4A is fine. I have similar specs on the power brick I use for my QC.
However, that brick is center-pin-positive. The QC’s power input is center-pin-negative. You may damage your QC if you try to use that power brick as-is. You can get a polarity reverse cable pretty cheap on Amazon or through Voodoo Lab and it will safely convert to center-pin-negative for the QC.
The other thing is to make sure you’re matching the correct barrel size. QC has a 2.1mm pin, same as any Boss-style pedal. It’s not clear what size of connector your power brick has.
Hi there, thanks for the reply to my question. I’ve never even heard the term ‘centre-pin-negative’ but I’m going to take your word for it! I’ll look into buying a polarity reverse cable. By the way, has anyone on here ever commented on how thin and flimsy the QC power unit seems? Considering the unit itself is so well made and robust, it seems odd to supply a power source with such thin wire. Thank you again. S
I would definitely recommend having a backup PS just in case but I think you will be fine with the OEM, almost 4y without any issues for me.
This symbol right here will tell you if the power supply is center-pin negative or positive. Every power supply will have this somewhere. In your case, you have the positive being applied to the center (of the connector). This is the opposite of what the QC needs.
There has been endless debate over the perceived quality of the OEM power supply. But to back up @MP_Mod , it works well and the wire in it is sufficient to supply the current that the QC needs.
As for having a backup, make sure the connector end is a 2.1mm barrel connector so it will “grip” the pin of the QC appropriately. Center negative, 12V with a minimum of 2A (but more is OK), and you’re good to go.
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You can also cut the cable and invert the connection.
Ha, thank you. However, I have trouble changing a plug, so I wouldn’t trust myself to start cutting cables and inverting connections!
Couple of links if you’re interested. Here’s what I use. This setup has worked perfectly since day one, and it’s still going strong 4+ years later:
12V 3.34A (40W) power supply, 2.1mm plug, center-pin-positive:
https://www.jameco.com/z/GST40A12-P1J-MEAN-WELL-12-Volt-3340mA-40-Watt-3-Wire-Regulated-Switching-Desktop-Power-Adapter-2-1mm-Plug-Level-VI_2224307.html
…Combine that with a reverse polarity cable to make the center pin negative:
The power supply does not come with an IEC cable–the power cable that runs from the wall outlet to the brick. You would need to source one separately, but those are easy and inexpensive.
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thank you so much for your helpfulness. I’m in the UK so I’d have to find another supplier but it’s good to know what I need. Cheers.
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Yeah, there have been a lot of complaints about the QC’s power supply not being bulky and heavy enough. 
I did buy a spare OEM supply but, in 4 years, I’ve never had a failure. I don’t recall seeing a post from anyone who’s had a failure either. I do wish they’d used a better connector but, being mounted on a pedalboard, I’ve never had a problem with breakage or a pull-out.
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Ah thanks, that’s good to know. If there was a pull-out while using the QC, would it cause any problem do you know? It isn’t clear from the manual whether it was ok or not.
NDSP recommends that power cycling should be done via the main power button but you should be okay once in a while.
Originally, the word was that disconnecting power was okay, as long as you weren’t in the middle of a backup, firmware update, etc. 
I switched power from my pedalboard strip for 2+ years with no problem. That recommendation changed a while back so I stopped doing it. Regardless, I doubt that a random accidental disconnection (while idle) would be catastrophic, but should be avoided, if possible. Do you not intend to use a pedalboard?
Thanks for that helpful reply, Pete. I don’t use a pedal board but I’m just a bit worried that the lead might get stood on and pulled out in the middle of a gig – probably by myself!
I understand…hence the reason mine’s on a pedalboard. My big feet can do some serious damage!