🔋💻 IBM/Lenovo 20V 90W Laptop Charger
 
(20V 4.5A AC Adapter • 90W • 7.9 mm × 5.5 mm Barrel Connector • With Center Pin)

This robust AC adapter delivers 90W of regulated DC power to ThinkPads using the 7.9 mm × 5.5 mm barrel connector with a center pin. It was the standard supply for IBM’s final ThinkPads and Lenovo’s first generation, supporting mainstream business laptops through the mid‑2000s.
 
🔧 Charger Form
Input: 100–240V AC, 50/60Hz
Output: 20V DC, 4.5A (90W)
Connector: 7.9 mm outer / 5.5 mm inner barrel with center pin
Inline power brick with detachable AC cord
Often labeled as 92P1109, 92P1156, FRU 42T4428, or equivalent
 
🖥️ Compatible Devices
🖤 ThinkPad T‑Series
T40, T41, T42, T43
T60, T61
Early T400, T500
🖤 ThinkPad X‑Series
X30, X31, X32
X40, X41
X60, X61
🖤 ThinkPad R‑Series
R50, R51, R52
R60, R61
🖤 ThinkPad Z‑Series
Z60m, Z60t
Z61m, Z61t
🖤 ThinkPad A‑Series (late)
A30, A31 (20V configs)
🖤 Other IBM/Lenovo Models
Early SL‑Series (SL300, SL400, SL500)
Select ThinkPad docking stations with 7.9 mm barrel input
 
✅ Common Uses
🔌 Powering IBM/Lenovo ThinkPads with Pentium M, Core Duo, and Core 2 Duo CPUs
🧩 Replacing lost or damaged OEM 90W adapters
🏢 Standardizing spares for legacy ThinkPad fleets
🎒 Keeping as a travel adapter for collectors of transitional ThinkPads
🧪 Testing ThinkPads with a known‑good 90W supply
 
🧠 Signal Format
⚡ Input: Universal AC (100–240V)
🔋 Output: Regulated 20V DC, 90W max
🔌 Center pin provides ID signal for adapter recognition
🔁 Backward compatible with 65W ThinkPads (safe, charges faster)
 
⚠️ Things to Watch Out For
📉 Not suitable for Lenovo slim‑tip or USB‑C ThinkPads
🔌 Connector must match — not interchangeable with earlier 5.5 mm × 2.5 mm IBM barrels
🧯 Avoid third‑party clones with weak center pins — may cause “adapter not recognized” errors
🌀 Excess heat or frayed cables can cause intermittent charging
🧪 Always confirm laptop’s required wattage before swapping adapters
 
🛠️ Quick Tips for Beginners
🧭 Check underside of ThinkPad or original charger for voltage and connector size
🔌 Use only with laptops rated for 20V and 7.9 mm × 5.5 mm barrel input
🧪 If laptop reports “adapter not recognized,” inspect center pin and barrel contact
🧯 Label adapters clearly to avoid mix‑ups with slim‑tip chargers
🧵 Keep one at desk and one in travel bag for convenience