IBM 5150 - Power Supply Unit (PSU)
Warning #1
Turning off the power supply's big red switch does not remove AC mains (house) voltage from all components within the power supply. (Example)
With that information, some people may decide to also power off the 5150 at the wall socket.
Warning #2
Opening the 5150's PSU may expose you to hazardous voltages and currents. Do not assume that those hazards will disappear shortly after disconnecting the PSU from AC mains (house) power. Before opening the power supply, adequately educate yourself as to the hazards. Some hazard examples are at here.
Wattage - Breakdown
The IBM 5150's power supply is rated at approximately 63 Watts. Expressed that way, the wattage is misleading. For example, it does not mean that 63 Watts of power can be drawn from the +5V line if no power is drawn from the other lines. Each of the output voltage lines has its own power rating, that must not be exceeded. Click here to see those ratings.
Voltage Tolerances
See here.
Minimum Off Time
From the IBM 5150 Technical Reference: "When the power supply is turned on after it has been off for a minimum of 5 seconds, it generates a 'power good' signal that indicates there is adequate power for processing."
So, after turning off the power supply, wait at least 5 seconds if you are planning to turn it back on. Any shorter; the motherboard may not start up (due to lack of a POWER GOOD signal).
Start-Up Loading
The IBM 5150's power supply requires a sufficient load in order to start/operate.
In some cases of insufficient loading, the power supply starts (you see the fan turn) but the power supply stops after a second or so. In other cases, the fan won't even turn. Note however that both of those symptoms can also be produced by the power supply being overloaded by something.
The IBM 5150 motherboard alone is normally enough of a load to start/operate the IBM 5150's power supply. <----- 'Normally' is not the same as 'always'.
The Tandon full-height floppy drive alone is normally enough of a load to start/operate the IBM 5150's power supply. <----- 'Normally' is not the same as 'always'.
Known Use of the -5V by IBM
• RAM chips (4116 class) on the '16KB-64KB' version of IBM 5150 motherboard
• Chip U1 on both versions of IBM 5150 motherboard
• Expansion card: RAM chips (4116 class) on the 'IBM 32KB Memory Expansion Option'
• Expansion card: RAM chips (4132 class) on the 'IBM 64KB Memory Expansion Option'
• Expansion card: Early version of the 'IBM 5.25" Diskette Drive Adapter'
63.5W versus 63W
From what I have seen, the 110V units are usually labelled "63.5W" and the 220V units are usually labelled "63W". I have seen at least one exception.
Powering Motherboard Via Bench Top Power Supply
See here.
Circuit Diagram
IBM periodically used different variations of the PSU. Click here for a couple of variations.
Modifying a 120V AC unit to 230V/240V AC
See here.