In the old days, we just pulled the plug while the PC was running and that drained the caps. But now, they have under voltage protection and it doesn't work. At least your PSU should have that safety feature. This is why you don't buy cheap PSUs. The cheapest PSU I know of that is safe and won't destroy your PC if something happens is the Thermaltake 500W White for $40 on Amazon. But if it has a fault, it will most likely brick the PSU. Go up to around $60 and you can get a midrange 500W EVGA PSU. 500W is more than most gamers need actually. Unless you have high end PC money. you can run a Ryzen 5800X3D and a 7900XT or 4080 on a quality 500W PSU, assuming you don't plan to OC. And having way more than you need is not better. I think it just opens up the possibility of doing a lot more damage. Yes, modern PSUs of high quality have a lot of different kinds of circuit protection built in. But, like the circuit breaker in your house, it isn't really designed to actually protect things that are plugged in, even though 99 times out of 100 it will do just that. But there is always a chance that a fault could keep getting fed power because the PSU just doesn't see it. It cannot measure the individual circuit voltages in your GPU. Yes, I know, those have gotten rather sophisticated too and, well, the fact is things don't always go as planned and no matter how many different faults they consider, they could always miss something, or rather, likely not protect against all possibilities due to time and cost reasons. With a properly sized PSU, you might get a puff of smoke and need to do a little board repair. But there's always the possibility an overkill PSU could turn the whole thing into a flaming mess before shutting off. If you have to open up a PSU RFN and can't wait a couple hours for the big, scary electrolytic caps to bleed off charge, you need to keep it plugged in (power switch OFF) and shunt all the big caps to ground. Then you unplug it and proceed. Or you could just wear gloves that are suitable insulation for whatever power they put out and not even worry about it. Or you could just not touch any of the capacitor leads. Pretty basic stuff and I could totally clean a PSU and change the fan without getting zapped. Above all, don't stick both hands inside at the same time. If you do get zapped, you don't want the conduction path going through the heart. You can take a lot more of a jolt and survive if it doesn't. I used to be a commercial aircraft tech. The ignition system on a large jet engine is extremely dangerous. It definitely WILL kill you. Next to that, the caps in your PSU or even the flyback on a CRT pales in comparison. I've been shocked by 120V AC a few times. I've hot wired an outlet bare-handed a time or two without getting shocked as well. TL;DR, the best insurance against getting shocked when working on a PSU is a pair of lineman's gloves. You can get a quality pair of relatively thin class 0 rated gloves from Uline for around $100, depending on size. Class 0 is rated for up to 1000V. You could bungle around inside a live PSU all day long and be totally fine. In fact, you could make do with Class OO. You'd need a Class 3 to comfortably protect you against a 25kV flyback circuit. No, the current doesn't matter because with no potential difference (voltage), there is no current flow. However, the properties and thickness of a material determines how much of a potential difference is required to arc through it. This property is called resistivity.
In the old days, we just pulled the plug while the PC was running and that drained the caps. But now, they have under voltage protection and it doesn't work. At least your PSU should have that safety feature. This is why you don't buy cheap PSUs. The cheapest PSU I know of that is safe and won't destroy your PC if something happens is the Thermaltake 500W White for $40 on Amazon. But if it has a fault, it will most likely brick the PSU. Go up to around $60 and you can get a midrange 500W EVGA PSU. 500W is more than most gamers need actually. Unless you have high end PC money. you can run a Ryzen 5800X3D and a 7900XT or 4080 on a quality 500W PSU, assuming you don't plan to OC. And having way more than you need is not better. I think it just opens up the possibility of doing a lot more damage. Yes, modern PSUs of high quality have a lot of different kinds of circuit protection built in. But, like the circuit breaker in your house, it isn't really designed to actually protect things that are plugged in, even though 99 times out of 100 it will do just that. But there is always a chance that a fault could keep getting fed power because the PSU just doesn't see it. It cannot measure the individual circuit voltages in your GPU. Yes, I know, those have gotten rather sophisticated too and, well, the fact is things don't always go as planned and no matter how many different faults they consider, they could always miss something, or rather, likely not protect against all possibilities due to time and cost reasons.
With a properly sized PSU, you might get a puff of smoke and need to do a little board repair. But there's always the possibility an overkill PSU could turn the whole thing into a flaming mess before shutting off.
If you have to open up a PSU RFN and can't wait a couple hours for the big, scary electrolytic caps to bleed off charge, you need to keep it plugged in (power switch OFF) and shunt all the big caps to ground. Then you unplug it and proceed. Or you could just wear gloves that are suitable insulation for whatever power they put out and not even worry about it. Or you could just not touch any of the capacitor leads. Pretty basic stuff and I could totally clean a PSU and change the fan without getting zapped. Above all, don't stick both hands inside at the same time. If you do get zapped, you don't want the conduction path going through the heart. You can take a lot more of a jolt and survive if it doesn't.
I used to be a commercial aircraft tech. The ignition system on a large jet engine is extremely dangerous. It definitely WILL kill you. Next to that, the caps in your PSU or even the flyback on a CRT pales in comparison. I've been shocked by 120V AC a few times. I've hot wired an outlet bare-handed a time or two without getting shocked as well.
TL;DR, the best insurance against getting shocked when working on a PSU is a pair of lineman's gloves. You can get a quality pair of relatively thin class 0 rated gloves from Uline for around $100, depending on size. Class 0 is rated for up to 1000V. You could bungle around inside a live PSU all day long and be totally fine. In fact, you could make do with Class OO.
You'd need a Class 3 to comfortably protect you against a 25kV flyback circuit. No, the current doesn't matter because with no potential difference (voltage), there is no current flow. However, the properties and thickness of a material determines how much of a potential difference is required to arc through it. This property is called resistivity.